Documents published in 2020 : Scipedia

Steel Corrosion in a Chloride Contaminated Concrete Pore Solution with Low Oxygen Availability
L. Toro, C. Andrade, J. Fullea, I. Martínez, N. Rebolledo

(2011). Advances in Modeling Concrete Service Life. RILEM Bookseries, vol 3, pp. 53-63. Springer, Dordrecht

Abstract
It is commonly mentioned that in concrete chloride induced corrosion is controlled by the oxygen content in such a manner that in water saturated conditions no oxygen will be present and thus no corrosion can develop. In the present paper, experimentation has been made in low oxygen availability “pore” solutions with several amounts of chlorides. These situations may represent the case of a water saturated concrete. The results indicate that at very low oxygen contents, i.e. almost negligible because complete removal is very difficult, corrosion may develop in presence of chlorides. The presence or absence of corrosion is influenced by the amount of chloride, its corrosion potential and the steel surface condition.
Abstract
It is commonly mentioned that in concrete chloride induced corrosion is controlled by the oxygen content in such a manner that in water saturated conditions no oxygen will [...]
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From corrosion rate to accumulated corrosion depth or loss in cross section of reinforcements
N. Rebolledo, C. Andrade

(2011). Advances in Modeling Concrete Service Life. RILEM Bookseries, vol 3, pp. 43-51. Springer, Dordrecht

Abstract
In marine environments, reinforcement corrosion develops due to the penetration of chlorides through the concrete pores. Initially the corrosion appears as localized attack, but when the chlorides arrive in high quantities, it extends to the bar surfaces which corrode entirely. In numerous previous studies, the detection of corrosion and its evolution have been monitored by means of measuring and presenting the variation of corrosion rate over time. This representation can be used to deduce when corrosion initiates on a steel bar and how it evolves with time. However, as the corrosion rate changes with temperature and the corrosion process itself evolves, this representation may not be clear enough to be used for comparative purposes. The present work proposes a parallel use of accumulated corrosion depth, which is obtained by the integration of each age of the corrosion rate-time curve. This kind of representation enables the determination of corrosion depth at each age and appears more appropriate for comparative purposes. The procedure is applied to concrete specimens that have been in contact with natural sea water from the Mediterranean Sea for 20 years. The specimens are prepared with different binders in different proportions for purposes of comparison.
Abstract
In marine environments, reinforcement corrosion develops due to the penetration of chlorides through the concrete pores. Initially the corrosion appears as localized attack, [...]
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Corrosion Data Interpretation in Concrete Structures
C. Andrade

(2011). Advances in Modeling Concrete Service Life. RILEM Bookseries, vol 3, pp. 1-10. Springer, Dordrecht

Abstract
Concrete protects the steel embedded until carbonation front or the chloride threshold reaches the rebar. Then a corrosion process develops. In present paper the corrosion process is analyzed from its onset a definition of which is given. The techniques for its measurement are described and also are given a model for the corrosion propagation period as well as some alternatives to assume a value of the corrosion rate, even based in the values of the concrete resistivity. Finally, the functions of relation between the corrosion and the structural consequences are commented.
Abstract
Concrete protects the steel embedded until carbonation front or the chloride threshold reaches the rebar. Then a corrosion process develops. In present paper the corrosion [...]
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From the instantaneous corrosion rate to a representative value
C. Andrade, N. Rebolledo, F. Pedrosa

ICCRRR 2012 (2012).

Abstract
Reinforcement corrosion develops due to the penetration of chlorides or of the carbonation front through the concrete pores and corrosion develops if enough moisture is present. However as the corrosion rate changes with temperature and the evolution of the corrosion itself, the representation may not be clear enough to be used for comparative purposes or for prediction of future evolution. The present work proposes a parallel use of accumulated corrosion depth, which is obtained by the integration of each age of the corrosion rate-time curve. This kind of representation enables the determination of corrosion depth at each age and appears the adequate to establish a Representative annual average value for comparative purposes. The procedure is applied to concrete specimens and real size elements exposed to Madrid outdoor conditions.
Abstract
Reinforcement corrosion develops due to the penetration of chlorides or of the carbonation front through the concrete pores and corrosion develops if enough moisture is present. [...]
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Corrosión y protección de armaduras
C. Andrade

Informes de la Construcción (1982). Vol. 33 (339), pp. 33-41

Abstract
La investigación en el campo de la corrosión de armaduras ha ido siempre muchos años con retraso respecto de los avances conseguidos en otros campos de la corrosión del acero, principalmente por la dificultad que supone el manejo de un electrólito (fase acuosa) que está encerrado en los poros de una estructura pétrea que dificulta el seguimiento visual de los procesos. Electrólito que evoluciona constantemente en el tiempo debido a la progresiva hidratación del cemento y, por lo tanto, no presenta una composición definida y fácilmente reproducible en todos sus componentes.
Abstract
La investigación en el campo de la corrosión de armaduras ha ido siempre muchos años con retraso respecto de los avances conseguidos en otros campos de [...]
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Determinación electroquímica cuantitativa de la velocidad de corrosión de un acero de construcción. Evaluación de la susceptibilidad al ataque por picaduras. Parte II: Ensayos en mortero
C. Andrade, J. González

Materiales de Construcción (1978). Vol. 28 (169), pp. 49-62

Abstract
El estudio del efecto de un determinado aditivo sobre la corrosión de las armaduras, o el de un hormigón con fisuras, o sometido a ambientes marinos o, en fin, de cualquier factor o circunstancia calificada como agresiva, suele exigir un laborioso y extenso programa de trabajo que contemple todas las posibilidades por las que puedan pasar las armaduras y el hormigón que las contiene. En éste, como en tantos otros campos de la tecnología, es importante la búsqueda de métodos de ensayo acelerados, que sean a la vez de lo más representativos posible una ayuda para economizar esfuerzo y materiales.
Abstract
El estudio del efecto de un determinado aditivo sobre la corrosión de las armaduras, o el de un hormigón con fisuras, o sometido a ambientes marinos o, en fin, [...]
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Corrosión de armaduras embebidas en hormigón carbonatado
C. Andrade, S. Algaba, J. González

Materiales de Construcción (1981). Vol. 31 (181), pp. 45-53

Abstract
Los componentes ácidos de la atmósfera, en particular el CO2, pueden neutralizar (carbonatar) el electrólito que llena los poros del hormigón y las fases del clínker, transformándolos en variedades del CO3Ca. La carbonatación no sólo modifica la estructura de la pasta de cemento y por lo tanto sus propiedades, sino que también tiene una influencia decisiva sobre la velocidad de corrosión de las armaduras (1) (2). En un reciente informe del Comité 12-CRC de la RILEM (3) se afirmaba que: "si se exceptúa la corrosión causada por Cl-, actualmente se está de acuerdo en que la carbonatación del hormigón es la condición esencial para la corrosión de las armaduras". (Aquí se debería añadir que esto se aplica a los hormigones simplemente armados, pues en los pretensados también es muy peligroso el fenómeno conocido como corrosión bajo tensión). La carbonatación puede desencadenar el proceso de corrosión, debido a que el descenso de pH que provoca hace posible el paso de las armaduras del estado pasivo al activo. La velocidad de ataque depende, sin embargo, de otros factores externos: un contenido mínimo de humedad en el medio ambiente que garantice la existencia del electrólito en los poros del hormigón, y un libre acceso de O2 hasta la superficie metálica para que pueda producirse la semirreacción catódica. Numerosos autores están de acuerdo con estos puntos, pero sin aportar pruebas cuantitativas de los mismos. Es objeto principal de este trabajo contribuir a llenar este vacío.
Abstract
Los componentes ácidos de la atmósfera, en particular el CO2, pueden neutralizar (carbonatar) el electrólito que llena los poros [...]
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La agresividad ambiental y la durabilidad de las estructuras de hormigón
B. Perepérez, E. Barberá, C. Andrade

Informes de la Construcción (2012). Vol. 38 (388), pp. 17-24

Abstract
The deterioration of concrete structures is the result of the interaction between them and the environment. In this study, comments are made on the most decisive environmental factors and their interactions. Special reference is made to the corrosion of the reinforcements and also to the different proposals of classification of the aggressiveness. El deterioro de las estructuras de hormigón es el resultado de la interacción entre ellas y el medio ambiente. En el presente trabajo se comentan los factores ambientales más determinantes y sus interacciones, con especial referencia a la corrosión de las armaduras, así como diferentes propuestas de clasificación de la agresividad.
Abstract
The deterioration of concrete structures is the result of the interaction between them and the environment. In this study, comments are made on the most decisive environmental [...]
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Corrosión de armaduras galvanizadas y sin proteger embebidas en cemento aluminoso estabilizado
M. Pérez, F. Triviño, C. Andrade

Materiales de Construcción (2012). Vol. 31 (182), pp. 49-68

Abstract
El cemento aluminoso, cuya obtención se basa en la fusión de bauxita y caliza, ha demostrado desde que fue patentado en Francia, en 1908 por Cementos Lafarge, unas propiedades excepcionales que lo hacen idóneo para ciertas aplicaciones. Tales propiedades son fundamentalmente el desarrollo de elevadas resistencias mecánicas en las primeras edades de hidratación, posibilidad de hormigonar en tiempo frío, una gran resistencia química al agua de mar y a los sulfatos, propiedades refractarias, etc. Todo ello hizo que el cemento aluminoso del tipo fundido, con un 40 % de Al2O3, se utilizara ampliamente en la construcción. Sin embargo, a partir de un determinado momento empezaron a observarse alteraciones en algunas obras construidas con hormigón de este tipo, manifestándose importantes pérdidas de sus resistencias mecánicas (1). Las causas de tales deterioros han sido ampliamente estudiadas (2)-(13), atribuyéndose la principal a la "conversión" de los aluminatos cálcicos hidratados hexagonales en hidratos cúbicos, según reacción [1]
Abstract
El cemento aluminoso, cuya obtención se basa en la fusión de bauxita y caliza, ha demostrado desde que fue patentado en Francia, en 1908 por Cementos Lafarge, [...]
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Gas distribution network topology problem
D. Brkić

Mathematica Balkanica (2012). 26 (3-4), 277-284

Abstract
Problem of gas fow in looped network is nonlinear problem and these kind of problems have to be solved using some kind of iterative procedure. For the pipeline network, two topology matrices can be written; i.e. loop matrix and node matrix. The node matrix is related to the first Kirchho 's law while the loop matrix is related to second Kirchho 's law. Here will be shown effcient method in which both matrices, i.e. the node and the loop matrix are united in one coherent procedure for solution of looped gas pipeline problem.
Abstract
Problem of gas fow in looped network is nonlinear problem and these kind of problems have to be solved using some kind of iterative procedure. For the pipeline network, two [...]
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Lambert W function in hydraulic problems
D. Brkić

Mathematica Balkanica (2012). 26 (3-4), 285-292

Abstract
Darcy’s flow friction factor is expressed in implicit form in some of the relations such as Colebrook’s and have to be solved by iteration procedure because the unknown friction factor appears on both sides of the equation. Lambert W function is implicitly elementary but is not, itself, an elementary function. Implicit form of the Lambert W function allows us to transform other implicit functions in explicit form without any kind of approximations or simplifications involved. But unfortunately, the Lambert W function itself cannot be solved easily without approximation. Two original transformations in explicit form of Colebrook’s relation using Lambert W function will also be shown. Here will be shown efficient procedure for approximate solutions of the transformed relations.
Abstract
Darcy’s flow friction factor is expressed in implicit form in some of the relations such as Colebrook’s and have to be solved by iteration procedure because the [...]
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Intelligent flow friction estimation
D. Brkić, Ž. Ćojbašić

Computational Intelligence and Neuroscience (2016). 2016, article 5242596

Abstract
Nowadays, the Colebrook equation is used as a mostly accepted relation for the calculation of fluid flow friction factor. However, the Colebrook equation is implicit with respect to the friction factor (). In the present study, a noniterative approach using Artificial Neural Network (ANN) was developed to calculate the friction factor. To configure the ANN model, the input parameters of the Reynolds Number (Re) and the relative roughness of pipe () were transformed to logarithmic scales. The 90,000 sets of data were fed to the ANN model involving three layers: input, hidden, and output layers with, 2, 50, and 1 neurons, respectively. This configuration was capable of predicting the values of friction factor in the Colebrook equation for any given values of the Reynolds number (Re) and the relative roughness () ranging between 5000 and 108 and between 10−7 and 0.1, respectively. The proposed ANN demonstrates the relative error up to 0.07% which had the high accuracy compared with the vast majority of the precise explicit approximations of the Colebrook equation.
Abstract
Nowadays, the Colebrook equation is used as a mostly accepted relation for the calculation of fluid flow friction factor. However, the Colebrook equation is implicit with [...]
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A note on explicit approximations to Colebrook’s friction factor in rough pipes under highly turbulent cases
D. Brkić

International Journal of Heat and Mass Transfer (2016). 93, 513-515

Abstract
New explicit approximations to the implicitly given Colebrook equation for flow friction factor are given. They are with improved accuracy compared with the one recently published [Shaikh et al.: Int. J. Heat Mass Tran. 88 (2015) 538–543]. The new approximations are highly accurate only in rough pipes under fully developed turbulent cases of flow.
Abstract
New explicit approximations to the implicitly given Colebrook equation for flow friction factor are given. They are with improved accuracy compared with the one recently published [...]
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Spreadsheet-based pipe networks analysis for teaching and learning purpose
D. Brkić

Spreadsheets in Education (eJSiE) (2016). 9 (2), article 4646

Abstract
An example of hydraulic design project for teaching purpose is presented. Students’ task is to develop a looped distribution network for water (i.e. to determinate node consumptions, disposal of pipes, and finally to calculate flow rates in the network’s pipes and their optimal diameters). This can be accomplished by using the original Hardy Cross method, the improved Hardy Cross method, the node-loop method, etc. For the improved Hardy Cross method and the node-loop method, use of matrix calculation is mandatory. Because the analysis of water distribution networks is an essential component of civil engineering water resources curricula, the adequate technique better than the hand-oriented one is desired in order to increase students’ understanding of this kind of engineering systems and of relevant design issues in more concise and effective way. The described use of spreadsheet solvers is more than suitable for the purpose, especially knowing that spreadsheet solvers are much more matrix friendly compared with the hand-orientated calculation. Although matrix calculation is not mandatory for the original Hardy Cross method, even in that case it is preferred for better understanding of the problem. The application of commonly available spreadsheet software (Microsoft Excel) including two real classroom tasks is presented.
Abstract
An example of hydraulic design project for teaching purpose is presented. Students’ task is to develop a looped distribution network for water (i.e. to determinate node [...]
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Study on the impacts of possible amendments to the ATEX, the Machinery, and the Pressure Equipment Directives with respect to equipment intended for use in the offshore oil and …
A. Aznárez, D. Brkić, S. Contini, M. Christou, S. Tarantola

(2016). Publications Office of the European Union

Abstract
The purpose of this study is to provide the Commission with the information necessary for the assessment of the economic, social, and environmental impacts of a possible extension of the scope of the EU product safety legislation (ATEX Directive 2014/34/EU, Pressure Equipment Directive 2014/68/EU and Machinery Directive 2006/42/EC) with respect to equipment intended for the use in the offshore oil and gas industry. Whereas equipment on fixed units is in the scope of these three Directives, mobile offshore units and equipment installed on them are currently in general excluded. In addition the Pressure Equipment Directive excludes also well-control equipment. The study investigates whether there are safety issues which could be addressed by extending the scope of the Directives and what would be the impacts of such an extension. Title Study on the impacts of possible amendments to the ATEX, the Machinery, and the Pressure Equipment Directive with respect to equipment intended for use in the offshore oil and gas industry.
Abstract
The purpose of this study is to provide the Commission with the information necessary for the assessment of the economic, social, and environmental impacts of a possible extension [...]
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Evolutionary optimization of Colebrook’s turbulent flow friction approximations
D. Brkić, Ž. Ćojbašić

Fluids (2017). 2 (2), article 15

Abstract
This paper presents evolutionary optimization of explicit approximations of the empirical Colebrook’s equation that is used for the calculation of the turbulent friction factor (λ), i.e., for the calculation of turbulent hydraulic resistance in hydraulically smooth and rough pipes including the transient zone between them. The empirical Colebrook’s equation relates the unknown flow friction factor (λ) with the known Reynolds number (R) and the known relative roughness of the inner pipe surface (ε/D). It is implicit in the unknown friction factor (λ). The implicit Colebrook’s equation cannot be rearranged to derive the friction factor (λ) directly, and therefore, it can be solved only iteratively [λ = f(λ, R, ε/D)] or using its explicit approximations [λ≈f(R, ε/D)], which introduce certain error compared with the iterative solution. The optimization of explicit approximations of Colebrook’s equation is performed with the aim to improve their accuracy, and the proposed optimization strategy is demonstrated on a large number of explicit approximations published up to date where numerical values of the parameters in various existing approximations are changed (optimized) using genetic algorithms to reduce maximal relative error. After that improvement, the computational burden stays unchanged while the accuracy of approximations increases in some of the cases very significantly.
Abstract
This paper presents evolutionary optimization of explicit approximations of the empirical Colebrook’s equation that is used for the calculation of the turbulent friction [...]
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Solution of the implicit Colebrook equation for flow friction using Excel
D. Brkić

Spreadsheets in Education (eJSiE) (2017). 10 (2), article 4663

Abstract
Empirical Colebrook equation implicit in unknown flow friction factor (λ) is an accepted standard forcalculation of hydraulic resistance in hydraulically smooth and rough pipes. The Colebrook equation givesfriction factor (λ) implicitly as a function of the Reynolds number (Re) and relative roughness (ε/D) of innerpipe surface; i.e. λ0=f(λ0, Re, ε/D). The paper presents a problem that requires iterative methods for thesolution. In particular, the implicit method used for calculating the friction factor λ0is an application of fixed-point iterations. The type of problem discussed in this "in the classroom paper" is commonly encountered influid dynamics, and this paper provides readers with the tools necessary to solve similar problems. Students’task is to solve the equation using Excel where the procedure for that is explained in this “in the classroom”paper. Also, up to date numerous explicit approximations of the Colebrook equation are available where as an additional task for students can be evaluation of the error introduced by these explicit approximations λ≈f(Re,ε/D) compared with the iterative solution of implicit equation which can be treated as accurate.
Abstract
Empirical Colebrook equation implicit in unknown flow friction factor (λ) is an accepted standard forcalculation of hydraulic resistance in hydraulically smooth and [...]
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Unified friction formulation from laminar to fully rough turbulent flow
D. Brkić, P. Praks

Applied Sciences (2018). 8 (11), article 2036

Abstract
This paper provides a new unified formula for Newtonian fluids valid for all pipe flow regimes from laminar to fully rough turbulent flow.This includes laminar flow; the unstable sharp jump from laminar to turbulent flow; and all types of turbulent regimes, including the smooth turbulent regime, the partial non-fully developed turbulent regime, and the fully developed rough turbulent regime. The new unified formula follows the inflectional form of curves suggested in Nikuradse’s experiment rather than the monotonic shape proposed by Colebrook and White. The composition of the proposed unified formula uses switching functions and interchangeable formulas for the laminar, smooth turbulent, and fully rough turbulent flow regimes. Thus, the formulation presented below represents a coherent hydraulic model suitable for engineering use. This new flow friction model is more flexible than existing literature models and provides smooth and computationally cheap transitions between hydraulic regimes.
Abstract
This paper provides a new unified formula for Newtonian fluids valid for all pipe flow regimes from laminar to fully rough turbulent flow.This includes laminar flow; the unstable [...]
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Advanced iterative procedures for solving the implicit Colebrook equation for fluid flow friction
P. Praks, D. Brkić

Advances in Civil Engineering (2018). 2018, article 5451034

Abstract
The empirical Colebrook equation from 1939 is still accepted as an informal standard way to calculate the friction factor of turbulent flows (4000 < Re < 108) through pipes with roughness between negligible relative roughness (ε/D ⟶ 0) to very rough (up to ε/D = 0.05). The Colebrook equation includes the flow friction factor λ in an implicit logarithmic form, λ being a function of the Reynolds number Re and the relative roughness of inner pipe surface ε/D: λ = f(λ, Re, ε/D). To evaluate the error introduced by the many available explicit approximations to the Colebrook equation, λ ≈ f(Re, ε/D), it is necessary to determinate the value of the friction factor λ from the Colebrook equation as accurately as possible. The most accurate way to achieve that is by using some kind of the iterative method. The most used iterative approach is the simple fixed-point method, which requires up to 10 iterations to achieve a good level of accuracy. The simple fixed-point method does not require derivatives of the Colebrook function, while the most of the other presented methods in this paper do require. The methods based on the accelerated Householder’s approach (3rd order, 2nd order: Halley’s and Schröder’s method, and 1st order: Newton–Raphson) require few iterations less, while the three-point iterative methods require only 1 to 3 iterations to achieve the same level of accuracy. The paper also discusses strategies for finding the derivatives of the Colebrook function in symbolic form, for avoiding the use of the derivatives (secant method), and for choosing an optimal starting point for the iterative procedure. The Householder approach to the Colebrook’ equations expressed through the Lambert W-function is also analyzed. Finally, it is presented one approximation to the Colebrook equation with an error of no more than 0.0617%.
Abstract
The empirical Colebrook equation from 1939 is still accepted as an informal standard way to calculate the friction factor of turbulent flows (4000 < Re < 108) through [...]
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One-log call iterative solution of the Colebrook equation for flow friction based on Padé polynomials
P. Praks, D. Brkić

Energies (2018). 11 (7), article 1825

Abstract
The 80 year-old empirical Colebrook function ξ, widely used as an informal standard for hydraulic resistance, relates implicitly the unknown flow friction factor λ, with the known Reynolds number R e and the known relative roughness of a pipe inner surface ε*; λ= ξ (R e, ε*, λ). It is based on logarithmic law in the form that captures the unknown flow friction factor λ in a way that it cannot be extracted analytically. As an alternative to the explicit approximations or to the iterative procedures that require at least a few evaluations of computationally expensive logarithmic function or non-integer powers, this paper offers an accurate and computationally cheap iterative algorithm based on Padé polynomials with only one l o g-call in total for the whole procedure (expensive l o g-calls are substituted with Padé polynomials in each iteration with the exception of the first). The proposed modification is computationally less demanding compared with the standard approaches of engineering practice, but does not influence the accuracy or the number of iterations required to reach the final balanced solution
Abstract
The 80 year-old empirical Colebrook function ξ, widely used as an informal standard for hydraulic resistance, relates implicitly the unknown flow friction factor λ, [...]
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Choosing the optimal multi-point iterative method for the Colebrook flow friction equation
P. Praks, D. Brkić

Processes (2018). 6 (8), article 130

Abstract
The Colebrook equation is implicitly given in respect to the unknown flow friction factor λ; λ=ζ(Re, ε∗, λ)which cannot be expressed explicitly in exact way without simplifications and use of approximate calculus. A common approach to solve it is through the Newton–Raphson iterative procedure or through the fixed-point iterative procedure. Both require in some cases, up to seven iterations. On the other hand, numerous more powerful iterative methods such as threeor two-point methods, etc. are available. The purpose is to choose optimal iterative method in order to solve the implicit Colebrook equation for flow friction accurately using the least possible number of iterations. The methods are thoroughly tested and those which require the least possible number of iterations to reach the accurate solution are identified. The most powerful three-point methods require, in the worst case, only two iterations to reach the final solution. The recommended representatives are Sharma–Guha–Gupta, Sharma–Sharma, Sharma–Arora, Džuni´c–Petkovi´c–Petkovi´c; Bi–Ren–Wu, Chun–Neta based on Kung–Traub, Neta, and the Jain method based on the Steffensen scheme. The recommended iterative methods can reach the final accurate solution with the least possible number of iterations. The approach is hybrid between the iterative procedure and one-step explicit approximations and can be used in engineering design for initial rough, but also for final fine calculations.
Abstract
The Colebrook equation is implicitly given in respect to the unknown flow friction factor λ; λ=ζ(Re, ε∗, λ)which cannot be expressed [...]
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Symbolic regression-based genetic approximations of the Colebrook equation for flow friction
P. Praks, D. Brkić

Water (2018). 10 (9), article 1175

Abstract
Widely used in hydraulics, the Colebrook equation for flow friction relates implicitly to the input parameters; the Reynolds number, Re and the relative roughness of an inner pipe surface, ε/D with an unknown output parameter; the flow friction factor, λ; λ = f (λ, Re, ε/D). In this paper, a few explicit approximations to the Colebrook equation; λ≈f (Re, ε/D), are generated using the ability of artificial intelligence to make inner patterns to connect input and output parameters in an explicit way not knowing their nature or the physical law that connects them, but only knowing raw numbers, {Re, ε/D}→{λ}. The fact that the used genetic programming tool does not know the structure of the Colebrook equation, which is based on computationally expensive logarithmic law, is used to obtain a better structure of the approximations, which is less demanding for calculation but also enough accurate. All generated approximations have low computational cost because they contain a limited number of logarithmic forms used for normalization of input parameters or for acceleration, but they are also sufficiently accurate. The relative error regarding the friction factor λ, in in the best case is up to 0.13% with only two logarithmic forms used. As the second logarithm can be accurately approximated by the Padé approximation, practically the same error is obtained also using only one logarithm.
Abstract
Widely used in hydraulics, the Colebrook equation for flow friction relates implicitly to the input parameters; the Reynolds number, Re and the relative roughness of an inner [...]
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Accurate and efficient explicit approximations of the Colebrook flow friction equation based on the Wright ω-function: Reply to Discussion
D. Brkić, P. Praks

Mathematics (2019). 7 (5), article 410

Abstract
This reply gives two corrections of typographical errors in respect to the commented article, and then provides few comments in respect to the discussion and one improved version of the approximation of the Colebrook equation for flow friction, based on the Wright ω-function. Finally, this reply gives an exact explicit version of the Colebrook equation expressed through the Wright ω-function, which does not introduce any additional errors in respect to the original equation. All mentioned approximations are computationally efficient and also very accurate. Results are verified using more than 2 million of Quasi Monte-Carlo samples.
Abstract
This reply gives two corrections of typographical errors in respect to the commented article, and then provides few comments in respect to the discussion and one improved [...]
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Accurate and efficient explicit approximations of the Colebrook flow friction equation based on the Wright ω-function
D. Brkić, P. Praks

Mathematics (2019). 7 (1), article 34

Abstract
The Colebrook equation is a popular model for estimating friction loss coefficients in water and gas pipes. The model is implicit in the unknown flow friction factor, f . To date, the captured flow friction factor, f , can be extracted from the logarithmic form analytically only in the term of the Lambert W-function. The purpose of this study is to find an accurate and computationally efficient solution based on the shifted Lambert W-function also known as the Wright ω-function. The Wright ω-function is more suitable because it overcomes the problem with the overflow error by switching the fast growing term, y=W(ex), of the Lambert W-function to series expansions that further can be easily evaluated in computers without causing overflow run-time errors. Although the Colebrook equation transformed through the Lambert W-function is identical to the original expression in terms of accuracy, a further evaluation of the Lambert W-function can be only approximate. Very accurate explicit approximations of the Colebrook equation that contain only one or two logarithms are shown. The final result is an accurate explicit approximation of the Colebrook equation with a relative error of no more than 0.0096%. The presented approximations are in a form suitable for everyday engineering use, and are both accurate and computationally efficient.
Abstract
The Colebrook equation is a popular model for estimating friction loss coefficients in water and gas pipes. The model is implicit in the unknown flow friction factor, f . [...]
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Short overview of early developments of the Hardy Cross type methods for computation of flow distribution in pipe networks
D. Brkić, P. Praks

Applied Sciences (2019). 9 (10), article 2019

Abstract
Hardy Cross originally proposed a method for analysis of flow in networks of conduits or conductors in 1936. His method was the first really useful engineering method in the field of pipe network calculation. Only electrical analogs of hydraulic networks were used before the Hardy Cross method. A problem with flow resistance versus electrical resistance makes these electrical analog methods obsolete. The method by Hardy Cross is taught extensively at faculties, and it remains an important tool for the analysis of looped pipe systems. Engineers today mostly use a modified Hardy Cross method that considers the whole looped network of pipes simultaneously (use of these methods without computers is practically impossible). A method from a Russian practice published during the 1930s, which is similar to the Hardy Cross method, is described, too. Some notes from the work of Hardy Cross are also presented. Finally, an improved version of the Hardy Cross method, which significantly reduces the number of iterations, is presented and discussed. We also tested multi-point iterative methods, which can be used as a substitution for the Newton–Raphson approach used by Hardy Cross, but in this case this approach did not reduce the number of iterations. Although many new models have been developed since the time of Hardy Cross, the main purpose of this paper is to illustrate the very beginning of modeling of gas and water pipe networks and ventilation systems. As a novelty, a new multi-point iterative solver is introduced and compared with the standard Newton–Raphson iterative method.
Abstract
Hardy Cross originally proposed a method for analysis of flow in networks of conduits or conductors in 1936. His method was the first really useful engineering method in the [...]
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An efficient iterative method for looped pipe network hydraulics free of flow-corrections
D. Brkić, P. Praks

Fluids (2019). 4 (2), article 73

Abstract
The original and improved versions of the Hardy Cross iterative method with related modifications are today widely used for the calculation of fluid flow through conduits in loop-like distribution networks of pipes with known node fluid consumptions. Fluid in these networks is usually natural gas for distribution in municipalities, water in waterworks or hot water in district heating systems, air in ventilation systems in buildings and mines, etc. Since the resistances in these networks depend on flow, the problem is not linear like in electrical circuits, and an iterative procedure must be used. In both versions of the Hardy Cross method, in the original and in the improved one, the initial result of calculations in the iteration procedure is not flow, but rather a correction of flow. Unfortunately, these corrections should be added to or subtracted from flow calculated in the previous iteration according to complicated algebraic rules. Unlike the Hardy Cross method, which requires complicated formulas for flow corrections, the new Node-loop method does not need these corrections, as flow is computed directly. This is the main advantage of the new Node-loop method, as the number of iterations is the same as in the modified Hardy Cross method. Consequently, a complex algebraic scheme for the sign of the flow correction is avoided, while the final results remain accurate.
Abstract
The original and improved versions of the Hardy Cross iterative method with related modifications are today widely used for the calculation of fluid flow through conduits [...]
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Colebrook’s flow friction explicit approximations based on fixed-point iterative cycles and symbolic regression
D. Brkić, P. Praks

Computation (2019). 7 (3), article 48

Abstract
The logarithmic Colebrook flow friction equation is implicitly given in respect to an unknown flow friction factor. Traditionally, an explicit approximation of the Colebrook equation requires evaluation of computationally demanding transcendental functions, such as logarithmic, exponential, non-integer power, Lambert W and WrightΩ functions. Conversely, we herein present several computationally cheap explicit approximations of the Colebrook equation that require only one logarithmic function in the initial stage, whilst for the remaining iterations the cheap Padé approximant of the first order is used instead. Moreover, symbolic regression was used for the development of a novel starting point, which significantly reduces the error of internal iterations compared with the fixed value staring point. Despite the starting point using a simple rational function, it reduces the relative error of the approximation with one internal cycle from 1.81% to 0.156% (i.e., by a factor of 11.6), whereas the relative error of the approximation with two internal cycles is reduced from 0.317% to 0.0259% (i.e., by a factor of 12.24). This error analysis uses a sample with 2 million quasi-Monte Carlo points and the Sobol sequence.
Abstract
The logarithmic Colebrook flow friction equation is implicitly given in respect to an unknown flow friction factor. Traditionally, an explicit approximation of the Colebrook [...]
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What can students learn while solving Colebrook’s flow friction equation?
D. Brkić, P. Praks

Fluids (2019). 4 (3), article 114

Abstract
Even a relatively simple equation such as Colebrook’s offers a lot of possibilities to students to increase their computational skills. The Colebrook’s equation is implicit in the flow friction factor and, therefore, it needs to be solved iteratively or using explicit approximations, which need to be developed using different approaches. Various procedures can be used for iterative methods, such as single the fixed-point iterative method, Newton–Raphson, and other types of multi-point iterative methods, iterative methods in a combination with Padé polynomials, special functions such as Lambert W, artificial intelligence such as neural networks, etc. In addition, to develop explicit approximations or to improve their accuracy, regression analysis, genetic algorithms, and curve fitting techniques can be used too. In this learning numerical exercise, a few numerical examples will be shown along with the explanation of the estimated pedagogical impact for university students. Students can see what the difference is between the classical vs. floating-point algebra used in computers.
Abstract
Even a relatively simple equation such as Colebrook’s offers a lot of possibilities to students to increase their computational skills. The Colebrook’s equation [...]
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Accurate and Ecient Explicit Approximations of the Colebrook Flow Friction Equation Based on the Wright ω-Function: Reply to the Discussion by Majid Niazkar
P. Praks, D. Brkić

Mathematics (2020). 8(5), article 796

Abstract
In this reply, we present updated approximations to the Colebrook equation for flow friction. The equations are equally computational simple, but with increased accuracy thanks to the optimization procedure, which was proposed by the discusser, Dr. Majid Niazkar. Our large-scale quasi-Monte Carlo verifications confirm that the here presented novel optimized numerical parameters further significantly increase accuracy of the estimated flow friction factor.
Abstract
In this reply, we present updated approximations to the Colebrook equation for flow friction. The equations are equally computational simple, but with increased accuracy thanks [...]
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FIRE SIMULATIONS OF A FISHING RESEARCH VESSEL WITH FRP STRUCTURES
A. Tissari, T. Korhonen, T. Kling, A. Korkealaakso, T. Hakkarainen, T. Hakkarainen

International Conference Marine Design 2020 - Papers (2020).

Abstract
The fire safety effect of using fibre-reinforced polymer (FRP) as the primary construction material in a fishing research vessel was studied by fire simulations. The effect of FRP structures on fire development was assessed by comparing the simulated gas temperatures and potential heat releases with FRP and steel structures. The structural integrity of FRP structures was assessed using simulated temperatures of the structures as indicators of integrity. The effect of protective mineral wool and intumescent coating layers was also quantified. The results showed that despite the protection, the structural integrity of FRP bulkheads could be compromised in fire conditions. Mineral wool was found to be better protection than the intumescent coating: it can either prevent or postpone the pyrolysis of the FRP bulkhead, depending on the fire exposure.
Abstract
The fire safety effect of using fibre-reinforced polymer (FRP) as the primary construction material in a fishing research vessel was studied by fire simulations. The effect [...]
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Kuitulujitteisten muovien paloturvallisuus laivoissa / Fire safety of fibre-reinforced polymers in ships
T. Hakkarainen

Tuula Hakkarainen's personal collection (2020). 3

Abstract
Eurooppalaisen FIBRESHIP-tutkimusprojektin tavoitteena on kehittää suunnittelu- ja tuotantomenetelmäkokonaisuus, joka mahdollistaa yli 50 metrin pituisen laivan rungon ja kansirakenteen valmistamisen kuitulujitteisista muovikomposiiteista. Projektissa suoritettiin laaja kaksivaiheinen koeohjelma, jossa tutkittiin kuitulujitemuovimateriaalien ja -rakenteiden mekaanisia, väsymis- ja palo-ominaisuuksia. Tässä artikkelissa esitellään kuitulujitteisten muovikomposiittien pienen mittakaavan palokokeiden ja pyrolyysimallinnuksen tuloksia. Kuitulujitteisten muovien palo-ominaisuuksia voidaan parantaa merkittävästi paisuvilla pinnoitteilla. Pinnoitteet voivat muuttaa olennaisesti lämmön- ja savuntuottokäyrien muotoa, alentaa niiden maksimiarvoja ja pidentää syttymisaikaa. Vaikka palo-ominaisuudet ovat merkittävä tekijä kuitulujitteisten muovien käytössä laivateollisuudessa, myös muita näkökohtia kuten mekaaniset ja valmistustekniset ominaisuudet on otettava huomioon. Osa projektissa alustavasti tutkituista tuotteista ei päässyt jatkotarkasteluihin tästä syystä. Kokeissa tehdyt havainnot korostavat toistettavan ja hallitun valmistusprosessin tärkeyttä. Prosessi on ohjeistettava, valvottava ja raportoitava perusteellisesti. Laminaattien ja pinnoitteiden tulee olla tasalaatuisia, jotta kokeiden perusteella määritetyt palo-ominaisuudet voidaan varmistaa. Tarkat määrittelyt ja laadunvalvonta ovat keskeisessä roolissa, kun halutaan varmistaa materiaalien ja tuotteiden paloturvallisuus. Kovettujen hartsien massahäviö alkaa tyypillisesti vähän yli 300 °C:n lämpötilassa. Tällöin lujitemuovista tehty rakenne alkaa tuottaa palavia kaasuja ja myötävaikuttaa paloon. Lujitemuovien lasisiirtymälämpötilat ovat tyypillisesti 100 °C:n suuruusluokkaa. Tässä lämpötilassa materiaali pehmenee ja alkaa menettää kuormankantokykyään. Lujitemuoveista valmistetuilla rakenteilla on taipumus lämmetä paikallisesti, koska niiden lämmönjohtavuus on suhteellisen alhainen. Paikallisen palon tapauksessa keskeiset paloturvallisuusriskit ovat palavien kaasujen muodostuminen ja lämmöntuotto. Jos palo uhkaa suurta rakennetta, kuten osastopalon tapauksessa, pääongelma on materiaalin pehmeneminen ja kantokyvyn menetys.
Abstract
Eurooppalaisen FIBRESHIP-tutkimusprojektin tavoitteena on kehittää suunnittelu- ja tuotantomenetelmäkokonaisuus, joka mahdollistaa yli 50 metrin pituisen laivan [...]
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Fire performance assessment of FRP materials
T. Hakkarainen

Book of Proceedings - Nordic Fire and Safety Days 2018 (2018).

Abstract
The European FIBRESHIP research project aims to develop a comprehensive set of methods that would enable the building of the complete hull and superstructure of over 50-metre-long ships in fibre reinforced polymer (FRP) materials. In the work package dedicated to materials selection, an extensive experimental campaign is performed to characterize the fatigue and fire performance of a range of FRP materials and solutions. In this paper, the cone calorimetry results of FRP laminates are introduced in terms of ignitability, heat release, smoke production and effective heat of combustion. The fire performance of FRP materials can be considerably improved by suitable intumescent coatings. Coatings can significantly change the shape of the heat release and smoke production rate curves, and reduce their maximum values. Even though fire performance is of high importance in the use of FRP materials, also other properties, such as mechanical properties and manufacturing, need to be taken into account. In some cases, products with excellent fire performance have to be discarded from further considerations due to other issues.
Abstract
The European FIBRESHIP research project aims to develop a comprehensive set of methods that would enable the building of the complete hull and superstructure of over 50-metre-long [...]
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Estudio por SEM de los productos de corrosión de armaduras galvanizadas sumergidas en disoluciones de pH comprendido entre 12,6 y 13,6
M. Blanco-Varela, C. Andade, A. Macías

Materiales de Construcción (2012). Vol. 34 (195), pp. 55-66

Abstract
In previous work on galvanized reinforcements in contact with Ca-containing highly alkaline media, the authors have reported the existence of a threshold pH below whith such a medium is passivated, but at pH values above this it corrodes continuously until it totally disappears. In this paper, after a brief literature review concerning the identification of the corrosion products in these media, they report that the passivation detected from the data of the polarisation technique agreed with the results of an SEM study. They show that below the threshold pH value the surface is covered with a continuous layer of calcium hydroxyzincate, Ca[Zn(0II)j2-^ HjO, and above this pH, the layer increase its proportion of non-passivating ZnO, to the detriment of the calcium hydroxyzincate contents. They have also established that it is the (Ca^'^) ions that control the amount of calcium hydroxizincate formed, and therefore the likelihood of the formation of a continuous passivating layer. Finally, they report that if the calcium hydroxyzincate is perfectly developed, a later increase of the pH does not affect the stability.
Abstract
In previous work on galvanized reinforcements in contact with Ca-containing highly alkaline media, the authors have reported the existence of a threshold pH below whith such [...]
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FIBRESHIP - Paloturvallisia materiaaleja kevyisiin laivoihin / FIBRESHIP - Fire safe materials for lightweight ships
T. Hakkarainen

Tuula Hakkarainen's personal collection (2020). 1

Abstract
Kuituvahvisteisia polymeereja eli lujitemuoveja käytetään nykyisin laajalti kevyiden alusten runkorakenteissa, kun aluksen pituus on enintään 50 metriä. Näitä komposiittimateriaaleja käyttämällä voidaan saavuttaa suurempi lastikapasiteetti ja merkittäviä polttoainesäästöjä. Lujitemuovit eivät ruostu, mikä vähentää huoltotarvetta ja –kustannuksia. Niiden avulla voidaan myös parantaa laivan stabiilisuutta ja vähentää vedenalaista melua. Yli 50 metrin pituisissa aluksissa lujitemuovien käyttö on nykyisin kuitenkin rajoitettu sekundaarirakenteisiin ja –komponentteihin. Tämä johtuu pääosin näiden materiaalien kestävyyteen ja palo-ominaisuuksiin liittyvistä kysymyksistä, suunnittelu- ja tuotantomenetelmien kehitystarpeista sekä ohjeistuksen puutteesta. Euroopan unionin rahoittaman ”Engineering, production and life‐cycle management for the complete construction of large‐length fibre‐based ships” (FIBRESHIP) –tutkimushankkeen tavoitteena on mahdollistaa yli 50 metrin pituisten laivojen rungon ja kansirakenteiden rakentaminen muovikomposiiteista. FIBRESHIP-projektissa kehitetään innovatiivisia komposiittimateriaaleja laivateollisuuden tarpeisiin, laaditaan uusia suunnittelu- ja tuotantomenetelmiä ja –ohjeita sekä kehitetään ja validoidaan simulointityökaluja. FIBRESHIP-projekti alkaa toukokuussa 2017 ja kestää kolme vuotta. Projektiin osallistuu laivanrakennusteollisuutta, laivanvarustamoja, meriteknologia- ja komposiittimateriaaliyrityksiä, luokituslaitoksia ja tutkimuslaitoksia Espanjasta, Irlannista, Iso-Britanniasta, Italiasta, Kreikasta, Kyprokselta, Ranskasta, Romaniasta, Suomesta, Tanskasta ja Unkarista. Hankkeen koordinaattori on espanjalainen TSI (Técnicas y Servicios de Ingeniería). VTT on päävastuussa FIBRESHIP-projektissa kehitettävien komposiittimateriaalien ja -tuotteiden palo-ominaisuuksien arvioinnista palokokeiden ja simuloinnin avulla. VTT kehittää ja varmentaa numeerisia pyrolyysimalleja näille materiaaleille. VTT vastaa myös palomallinnuksen ja rakenteellisen analyysin yhdistävän simulointityökalun kehityksestä. Palotutkimuksen päivillä esitellään projektin tavoitteita, työsuunnitelmaa ja ensimmäisiä tuloksia elokuun 2017 tilanteen mukaisesti. Esityksessä keskitytään kehitettävien materiaalien ja tuotteiden palo-ominaisuuksiin, pyrolyysimallinnukseen ja palosimulointiin. Tämä projekti on saanut rahoitusta Euroopan unionin Horisontti 2020 –tutkimus- ja innovaatio-ohjelmasta perustuen rahoitussopimukseen nro 723360.
Abstract
Kuituvahvisteisia polymeereja eli lujitemuoveja käytetään nykyisin laajalti kevyiden alusten runkorakenteissa, kun aluksen pituus on enintään 50 metriä. [...]
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Durabilidad de las armaduras en el sistema Dragados-Plastbau
C. Andrade, J. Rodríguez

Informes de la Construcción (2012). Vol. 38 (383), pp. 49-53

Abstract
En un sistema de las características del presente, los elementos metálicos que pueden sufrir corrosión son principalmente la malla y los conectores que atraviesan el poliestireno. La porosidad del microhormigón y el no siempre suficiente espesor de recubrimiento pueden permitir una carbonatación del microhormigón que alcance la malla durante el período de vida útil previsto para la estructura. Este riesgo de corrosión por carbonatación viene acrecentado en este sistema particular por una posible aparición de fisuras (retracción, movimientos de dilatación y asentamientos diferenciales, etc.).
Abstract
En un sistema de las características del presente, los elementos metálicos que pueden sufrir corrosión son principalmente la malla y los conectores que [...]
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Rational approximation for solving an implicitly given Colebrook flow friction equation
P. Praks, D. Brkić

Mathematics (2020). 8 (1), artice 26

Abstract
The empirical logarithmic Colebrook equation for hydraulic resistance in pipes implicitly considers the unknown flow friction factor. Its explicit approximations, used to avoid iterative computations, should be accurate but also computationally efficient. We present a rational approximate procedure that completely avoids the use of transcendental functions, such as logarithm or non-integer power, which require execution of the additional number of floating-point operations in computer processor units. Instead of these, we use only rational expressions that are executed directly in the processor unit. The rational approximation was found using a combination of a Padé approximant and artificial intelligence (symbolic regression). Numerical experiments in Matlab using 2 million quasi-Monte Carlo samples indicate that the relative error of this new rational approximation does not exceed 0.866%. Moreover, these numerical experiments show that the novel rational approximation is approximately two times faster than the exact solution given by the Wright omega function.
Abstract
The empirical logarithmic Colebrook equation for hydraulic resistance in pipes implicitly considers the unknown flow friction factor. Its explicit approximations, used to [...]
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La importancia del curado en el comportamiento posterior frente a la corrosión de las estructuras de hormigón armado
W. López, S. Feliu, J. González, C. Andrade

Materiales de Construcción (2012). Vol. 41 (223), pp. 5-17

Abstract
Steel in contact with fresh concrete is covered by a layer of passivating oxydes due to the alkaline nature of the pore solution. The presence of oxygen plays an important role in this passivation process as well as in the corrosión one when is developped due to the ingress of aggressives, such as, chioride ions. In the present paper, results are commented on the behaviour found when oxygen is limited due to the concrete curing conditions, in a completely saturated chamber Surprisely, the results indícate that the oxygen availability during the curing has a marked influence on the future corrosión beabieviour This allows to deduce that the mechanisms involved are not so simple as was currently accepted and that new specific tests are needed to clarify the controversial points.
Abstract
Steel in contact with fresh concrete is covered by a layer of passivating oxydes due to the alkaline nature of the pore solution. The presence of oxygen plays an important [...]
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Study of corrosion rate variability in indoor and outdoor specimens
F. Pedrosa, C. Andrade

(2011). Advances in Modeling Concrete Service Life. RILEM Bookseries, vol 3, pp. 33-42. Springer, Dordrecht

Abstract
Behavior, time evolution and variability of the corrosion process in reinforced concrete structures is an important factor to have in mind if structural service life is to be determined. Corrosion development and its consequences over time are often empirically deduced. It would be significant to improve as much as possible the prediction accuracy of corrosion process behavior. In the present paper, a series of hygrothermal and corrosion data obtained for indoor and outdoor reinforced concrete specimens are summarized by means of descriptive statistics. For a T-beam exposed to continental weather conditions, temperature, relative humidity, corrosion potential and corrosion current density measurements were taken since the year of 1993. The same measurements were made for an outdoor pile exposed to the same conditions. The indoor studied specimens are two small slabs exposed to lab conditions for which corrosion measurements were taken in the first 96 days period. Chloride was added to the concrete mixture of one specimen in order to accelerate the corrosion process. Electrochemical corrosion rate measurements using modulated confinement of the current were taken by means of Gecor 8 system device. Temperature and relative humidity were measured both inside and outside of the outdoor specimen using a probe. Hygrothermal and corrosion results were plotted on time scale in order to visualize possible correlations. A first approach to a statistical analysis is made by describing the raw data obtained by means of average value and standard deviation for different variables. Results show that the accumulated corrosion progress linearly in time. In the outdoor exposed specimen two corrosion rates Icorr were noticed, being the highest for the first period where no cracks were yet produced. After cracking occurs corrosion rate decreases. No direct relation between RH and Icorr was observed.
Abstract
Behavior, time evolution and variability of the corrosion process in reinforced concrete structures is an important factor to have in mind if structural service life is to [...]
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Ruptures of prestressing cables
J. Balayssac, C. Andrade, J. Sánchez, H. Scheel

(2011). Non-Destructive Assessment of Concrete Structures: Reliability and Limits of Single and Combined Techniques. RILEM State of the Art Reports, Vol 1, pp. 305-334, Springer, Dordrecht

Abstract
The structures involved are prestressed concrete structures. The aim is to detect either failures of prestressing cables (or strands) or as a preventive measure to detect corrosion or damages before failure.
Abstract
The structures involved are prestressed concrete structures. The aim is to detect either failures of prestressing cables (or strands) or as a preventive [...]
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Corrosión del acero desnudo y galvanizado en yeso
M. Gómez, C. Andrade

Materiales de Construcción (2012). Vol. 38 (212), pp. 5-20

Abstract
Gypsum is a relatively lovi/-cost building material much abounding in our country. When it is put in contact with steel, it may produce high corrosion rates due to its pH value (close to 7). This work reports the results obtained in studying the corrosion rates of bare and galvanized steel in contact with gypsum and plaster, as well as the influence curing thermal treatment applied to gypsum, enviromental relative humidity and addition of compounds with different natures and purposes may have in such process. In-situ observations, as well as the measurement of the Polarization Resistance and the weight loss have been used as measurement technics. From the results obtained it has been possible to deduce that galvanized steel has better behaviour in dry enviroments than bare steel in the same conditions and moist atmosphere induces proportionally more corrosion in galvanized steel than in bare one. Additions to gypsum do not modified these conclusions, though it may be pointed out that addition of nitrites or lime improves the behaviour of bare steel, while galvanized behaviour is not modified. The addition of lime is not recommended because phenomena of dilated along time expansion may take place.
Abstract
Gypsum is a relatively lovi/-cost building material much abounding in our country. When it is put in contact with steel, it may produce high corrosion rates due to its pH [...]
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Influencia del contenido en álcalis de los cementos sobre la corrosión de armaduras galvanizadas
C. Andrade, A. Macías

Materiales de Construcción (2012). Vol. 31 (184), pp. 83-93

Abstract
Las armaduras galvanizadas han mostrado un comportamiento errático en los ensayos llevados a cabo hasta ahora, encontrándose en la literatura datos muy contradictorios. Los autores han encontrado que las siguientes tres variables tienen una decisiva importancia: a) pH del mortero u hormigón, que depende básicamente de la cantidad de álcalis del cemento, b) tipo de estructura metalográfica del recubrimiento galvanizado, que depende principalmente del tipo de acero y su contenido en Si y C, y c) la humedad contenida en los poros del hormigón. En este trabajo se presentan resultados relacionados sólo con el punto a). Se ha podido comprobar que existe un valor de pH umbral o crítico por encima del cual el recubrimiento galvanizado se corroe severamente, debido a la formación de capas no-protectoras de productos de corrosión. La evolución de la velocidad de corrosión se ha seguido mediante la Resistencia de Polarización, y las pérdidas de peso se han determinado también, gravimétricamente
Abstract
Las armaduras galvanizadas han mostrado un comportamiento errático en los ensayos llevados a cabo hasta ahora, encontrándose en la literatura datos muy contradictorios. [...]
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Estabilidad de la capa de hidroxizincato cálcico formada en las armaduras galvanizadas ante un posterior aumento del valor del pH
A. Macías, C. Andrade

Materiales de Construcción (2012). Vol. 36 (204), pp. 19-28

Abstract
In previous works on galvanized reinforcements in contact with Ca- containing highly alkaline media, the authors have reported the existence of a threshold pH of 13,3 ± 0,1, below which the Zn in contact with such a medium is passivated by formation of a continuous layer of calcium hydroxyzincate, but at pH values above this it corrodes continuously until it totally disappears. The investigation on the stability of the calcium hydroxyzincate layer after an increase of the pH to very high alkaline values, is the aim of the present paper. It has been establised that if the calcium hydroxyzincate is perfectly developed, a later increase of the pH does not affect the stability.
Abstract
In previous works on galvanized reinforcements in contact with Ca- containing highly alkaline media, the authors have reported the existence of a threshold pH of 13,3 ± [...]
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Corrosión de armaduras y su inspección en hormigones de cemento aluminoso
C. Andrade

Informes de la Construcción (2012). Vol. 44 (422), pp. 39-48

Abstract
Until recently has not become evident the magnitude of the problem that the corrosion of the reinforcement supposes for concrete technology. That is why, when aluminous cement preliminary degradations appeared it was not foreseen the dimension of future consequences..Now, the long term difficulty that aluminous cement presents is, in addition to the loss in mechanical strength, the possible corrosion of reinforcement. In present work are described aspects related to the processes which may originate the corrosion and given are some practical indications on how evaluate it.
Abstract
Until recently has not become evident the magnitude of the problem that the corrosion of the reinforcement supposes for concrete technology. That is why, when aluminous cement [...]
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Tendencias actuales en la investigación sobre corrosión de armaduras
C. Andrade

Informes de la Construcción (2012). Vol. 40 (398), pp. 7-14

Abstract
During the last 20 years, the corrosion of concrete rebars is increasily being considered a major problem due the high costs spent by some Governments on repair and of civil concrete structures. In the present paper, a brief description on the causes of this type of corrosion is offered together with some references to the costs of repairing of bridge decks published by USA researchs. Finally, the main lines of research which, in opinion of the authors have priority, are commented.
Abstract
During the last 20 years, the corrosion of concrete rebars is increasily being considered a major problem due the high costs spent by some Governments on repair and of civil [...]
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Report and database on the results of the fire performance experiments
T. Hakkarainen, A. Paajanen, J. García-Espinosa

Open Access Repository of the FIBRESHIP project (2020). 9

Abstract
Today, fibre reinforced polymer (FRP) materials are extensively used for building lightweight hull structures of vessels with length up to about 50 metres, whereas in longer vessels their use is limited to secondary structures and components. In the European FIBRESHIP research project, innovative FRP materials are evaluated, new design and production procedures and guidelines are elaborated, and new validated software analysis tools are developed. As a result of the project, a comprehensive set of methods will be compiled, enabling the building of the complete hull and superstructure of over 50-metre-long ships in FRP materials. The results enhance significantly the use of FRP materials in shipbuilding and strengthen the competitiveness of the European shipbuilding industry on the world market. In Task 2.4 of the FIBRESHIP project, an extensive experimental campaign was performed in two phases to characterize the fire performance of FRP materials and solutions. For the first phase, seven commercially available resins or resin systems were selected for examination of fire performance. Laminates with glass fibre reinforcement and cured resins without reinforcement were produced for cone calorimeter tests and thermogravimetric analyses, respectively. From these seven candidates, two materials were down-selected on the basis of the mechanical performance, manufacturability and impact (including cost, claimed fire retardancy, worker health impact and recyclability). The two material solutions chosen to continue to the second phase were LEO vinylester resin system and SR1125 epoxy resin system. The fire tests of the first phase showed that an intumescent coating on the surface of these laminates is essential for providing adequate fire performance. In the second phase, a more comprehensive evaluation of thermal and fire properties was performed by carrying out more cone calorimeter tests, as well as dynamic mechanical thermal analysis, microscale combustion calorimetry, differential scanning calorimetry and transient plane source tests. Simultaneously, data for pyrolysis modelling, thermomechanical modelling and fire simulation was produced. In cone calorimeter test at the irradiance of 50 kW/m2, the times to ignition of coated LEO and SR1125 were 75 and 52 seconds on the average, respectively. The maximum heat release was 261 kW/m2 for SR1125, but only 69 kW/m2 for LEO indicating good reaction-to-fire performance. The total heat release and the total smoke production were ca. 40 MJ/m2 and 9 m2, respectively, for both systems. Cone calorimeter tests of coated laminate specimens were run also at the irradiance levels of 25 and 35 kW/m2 and for specimens representing different production batches. The results were not consistent in all cases. In addition, DSC tests revealed changes of the glass transition temperature when the specimens were re-heated, referring to incomplete curing in the manufacturing process. These observations highlight the importance of repeatable and well- controlled manufacturing process. The whole process must be carefully instructed, monitored and reported. The laminates and coatings must be of uniform quality to ensure the fire performance claimed on the basis of fire tests performed. Precise specifications and quality control play a key role in securing the fire safety of materials and products. Thermogravimetric analyses and micro-scale combustion calorimetry showed that the mass loss of cured resins typically starts slightly above 300 °C both in inert (N2) and oxidative (air) atmosphere. The reactions in these atmospheres differ, the oxidative atmosphere revealing reactions such as char oxidation. At about 300 °C, however, a structure made of these FRP materials starts to produce combustible gases and contribute to fire. Dynamic mechanical thermal analysis showed that the glass transition temperature is ca. 111 °C for LEO, and ca. 95 °C for SR1125. In general, the glass transition temperatures of FRP materials are typically about 100 °C. At this temperature, the material softens and loses its loadbearing capacity. Structures made of FRP materials have a tendency to heat up locally, due to their relatively low thermal conductivity. In the case of a local fire, combustible gas production and heat release are the main concerns in terms of fire safety. If the fire threatens a large structure, like in the case of a compartment fire, the main problem is the softening of the material and the loss of the loadbearing capacity.
Abstract
Today, fibre reinforced polymer (FRP) materials are extensively used for building lightweight hull structures of vessels with length up to about 50 metres, whereas in [...]
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Análisis de las condiciones de fisuración en las estructuras de hormigón armado y su relación con la probabilidad de corrosión de las armaduras
J. Rodríguez, C. Andrade

Informes de la Construcción (2012). Vol. 36 (366), pp. 37-52

Abstract
Cracks appears in reinforced concrete structures as something inherent to the material they are composed. Causes of diverse kind advise to control this cracking, considering it can not be prevented. The durability of reinforcements is, till now, the reason that has determined, in most structures, the study and the control of this cracking. In this report, the information contained in certain standards in force (CP-110; ACI-318-83; B.A.E.L. 80; MODEL CODE AND EH-82) about the characteristics the concrete must have and about the cracking in pieces of reinforced concrete under pliability attempts, are analysed and resumed, trying to judge later its connection with the corrosion phenomenon in reinforcements
Abstract
Cracks appears in reinforced concrete structures as something inherent to the material they are composed. Causes of diverse kind advise to control this cracking, considering [...]
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FIBRESHIP Presentation delivered to academics, students and researchers at the "Composites at Bernal Seminar Series", Bernal Institute, University of Limerick, April 2019
A. Comer

Open Access Repository of the FIBRESHIP project (2020). 5

Abstract
Presentation given to Academics, students and researchers at the "Composites at Bernal Seminar Series", Bernal Institute, University of Limerick
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Testing and modelling chloride penetration into concrete
M. Prieto, P. Tanner, C. Andrade, F. Tavares, R. D'Andrea

Construction and Building Materials (2013). Vol. 39, pp. 9-18

Abstract
The design of concrete structures is usually made by means of a performance approach based on strength tests carried out following testing conditions agreed by convention. A similar approach should also be followed in the case of durability design regarding reinforcement corrosion. This type of consideration enables the establishment of verification of durability in categories. Three categories have been identified: (I) it would be the prescriptive method already given in present codes based on “deemed-to-satisfy” rules, (II) this is based in the testing through “durability indicators” that where still not quantification of the time to reach a limit state is explicit but the minimum life time is assured through performance based tests, (III) it is the category in which the calculation of aggressive ingress through models having explicit the time is made including probabilistic treatments. In the paper in addition to the comment on the most common methods of calculation of the chloride ingress and their limitations it is illustrated how for level II and III the measurement of the electrical resistivity results a very suitable proposal due to this parameter can be measured in a non-destructive test and serves to quality control. It is not only a performance test (level II) but it can be included in models of both the initiation and propagation periods. For the time to corrosion onset, the electrical resistivity represents the porosity and its connectivity and therefore can be used to model transport processes. It also results very suitable for measuring concrete aging and then accounting for the reduction of the diffusion coefficient with time. Concerning the propagation period, the electrical resistivity is an indication of the moisture content of concrete and therefore, it has a certain relationship with the corrosion cement. A model is proposed in which the resistivity is introduced in the square root of time law. Finally the paper comments on the tests methods used for the measurement of the diffusion coefficient and of resistivity
Abstract
The design of concrete structures is usually made by means of a performance approach based on strength tests carried out following testing conditions agreed by convention. [...]
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Linking fresh and durability properties of paste to SCC mortar
H. Figueiras, S. Nunes, J. Coutinho, C. Andrade

Cement and Concrete Research (2014). Vol. 45, pp. 209-226

Abstract
In the last years many approaches to design SCC have been developed, but it remains a very complex process since it is necessary to manipulate several variables and understand their effects on concrete behaviour (fresh and hardened state). The prediction of concrete or mortar behaviour based on paste properties will be a significant contribution to simplify SCC design. With this purpose, two statistical experimental designs were carried out, one at paste level and the other at mortar level, to mathematically model the influence of mixture parameters on fresh and durability properties. The derived numerical models were used to define an area, labelled by self-compacting zone at paste level (SCZ), where fresh properties of the paste enable the design of SCC mortar. Furthermore, in order to extend this link to durability properties, the effect of including aggregate in cement paste was evaluated by means of the electrical resistivity test.
Abstract
In the last years many approaches to design SCC have been developed, but it remains a very complex process since it is necessary to manipulate several variables and understand [...]
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The Eurocode 2 and the assessment of concrete structures with corroded reinforcement
J. Rodríguez, C. Andrade, D. Izquierdo, P. Tanner

Hormigón y Acero (2014). Vol. 65 (272), pp. 123-132

Abstract
The reinforcement corrosion is one of the major problems with relevant economic impact in the life cycle of concrete structures and that is why it is necessary to optimize the repair strategies in corroded structures. However, almost no international codes are available for structural evaluation and some criteria will be included in the revision of Eurocode 2 to evaluate existing deteriorated structures. A summary of Contecvet project funded EC is presented in this paper as well as some more recent developments. A first step in the evaluation of existing structures is to identify if the aggressive has reached the reinforcement and how much has affected to the structural performance. As soon as the corrosion rate has been calculated from the data taken in the structure, it is possible to estimate the rate of the structural deterioration process through the developed models and the remaining service life. Some models and expressions are summarized to estimate the residual bearing capacity of concrete structures with corroded reinforcement to be considered when drafting the new Eurocode 2.
Abstract
The reinforcement corrosion is one of the major problems with relevant economic impact in the life cycle of concrete structures and that is why it is necessary to optimize [...]
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Proposed amendment of concrete durability criteria in Eurocode 2
C. Andrade, R. Martínez, M. Sanjuán

Hormigón y Acero (2014). Vol. 65 (272), pp. 133-140

Abstract
The CEN/TC 250/SC2 and TC104/SC1 Committees have established a Joint Working Group, JWG TC250/TC104, in order to review all the durability aspects related to durability in Eurocode 2 “concrete structures” and EN 206-1 “concrete” standard. This JWG has studied the possibility of classifying concrete, not only by mechanical strength, but also by durability. This JWG has proposed that this classification be based on a direct test of carbonation or chloride resistance, which would oblige to make these types of tests routine in the future. As an alternative, the Spanish Mirror group has proposed to make this classification first by concrete mix proportioning as it is currently made and, in order to advance to a performance-based approach, by an indirect test (Durability Indicator). In present paper, the Spanish proposal is described and compared to that presented in the JWG. Advantages and disadvantages of both proposals are discussed and two Tables are presented that summarize what has been submitted by the AENOR CTN-140/SC2 for the revision of Chapter 4 of the Eurocode 2
Abstract
The CEN/TC 250/SC2 and TC104/SC1 Committees have established a Joint Working Group, JWG TC250/TC104, in order to review all the durability aspects related to durability in [...]
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Modelling the concrete‐real environment interaction to predict service life
C. Andrade

Structural Concrete (2015). Vol. 16 (2), pp. 1-2
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Recent durability studies on concrete structure
S. Tang, Y. Yao, C. Andrade, Z. Li

Cement and Concrete Research (2015). Vol. 78 (Part A), pp. 143-154

Abstract
The durability of concrete has attracted significant attention over the past several decades and is still a research hotspot until now. This paper reviews and discusses recent research activities on the durability of concrete, including: 1) major durability problems such as alkali aggregate reaction, sulfate attack, steel corrosion and freeze–thaw; 2) durability of concrete in marine environment; and 3) coupling effects of mechanical load and environmental factors on durability of concrete. Moreover, the consideration of durability in concrete structure design (DuraCrete and performance-based specifications) is also briefly reviewed.
Abstract
The durability of concrete has attracted significant attention over the past several decades and is still a research hotspot until now. This paper reviews and discusses [...]
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Influence of Crack Width on Long Term Degradation of Concrete Structures
J. Torres, C. Andrade

(2014). Durability of Reinforced Concrete from Composition to Protection. Springer, Cham

Abstract
The study of the influence of concrete crack width on corrosion of steel reinforcement due to exposure to aggressive environments is very important for durability design. Premature failure of structures may eventually occur during their service life. Since cracks in the concrete cover are inevitable due to the stress structures are subjected to, penetration of aggressive substances will occur more rapidly in cracked areas than in areas without cracking. This study addresses the corrosion effects on the reinforcement in cracked areas. Reinforced beams 2 m long and cracked at half-length with widths up to 1 mm were prepared 20 years ago, exposed to carbonation and chlorides and kept outdoors sheltered from rain until present. After 20 years, the carbonation depth in the faces of the cracks, and the reinforcement at the crack region have been examined. The results indicated that flexural cracks in high quality carbonated concrete present only a small additional risk of corrosion which, however, is significant in the presence of chlorides
Abstract
The study of the influence of concrete crack width on corrosion of steel reinforcement due to exposure to aggressive environments is very important for durability design. [...]
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Multiple linear regression model for the assessment of bond strength in corroded and non-corroded steel bars in structural concrete
M. Prieto, P. Tanner, C. Andrade

Materials and Structures (2016). Vol. 49, pp. 4749-4763

Abstract
With the growth and ageing of the stock of existing structures, structural assessment and retrofitting are fast acquiring a significant role in the construction industry. The benefits of upgrading existing reinforced concrete (RC) structures or extending their service life and of ensuring greater durability in designs for de novo construction have led to a need to include deterioration as a factor in structural safety models. Bond between reinforcing steel and concrete is of cardinal importance in this respect. The present paper proposes a unified formulation for assessing bond strength in corroded and non-corroded steel bars, and an associated model to accommodate the effect of transverse pressure where appropriate. The formulation is the result of applying multiple linear regression analysis to a database built from the findings of over 650 bond tests on corroded and non-corroded reinforcing steel reported in the literature. The data collected include a wide range of variables affecting bond strength, such as bar diameter, concrete compressive strength, concrete cover, anchorage length, confinement ratio and cross-sectional loss. A number of statistical criteria are used to compare the proposed formulation to the other bond strength assessment models, including the fib Model Code 2010 proposal for corroded steel bars. Further to the statistical tests conducted, the model proposed can be usefully applied to assess the structural safety of corroded RC members.
Abstract
With the growth and ageing of the stock of existing structures, structural assessment and retrofitting are fast acquiring a significant role in the construction industry. [...]
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Estimating corrosion attack in reinforced concrete by means of crack opening
C. Andrade, A. Cesetti, G. Mancini, F. Tondolo

Structural Concrete (2016). Vol. 17 (4), pp. 533-540

Abstract
The corrosion of reinforcement in concrete is the most common degradation phenomenon of reinforced concrete structures. Reinforced concrete elements subjected to corrosion generally crack due to the expansive nature of oxides. One very important task is estimating the corrosion level using a non‐destructive method in order to establish both the actual safety of the structure and a priority intervention plan. Many researchers have studied the relationship between the corrosion phenomenon and the corresponding crack openings and their evolution; several statistical analyses, based on test data from experimental campaigns under a wide range of test conditions, are available. The present work attempts to contribute to finding a relationship between the crack opening and the amount of corrosion induced in the reinforcing bars. The result of the analysis is that only a reduced number of tests can be used to establish an empirical model based on a reliable set of test data. A simple relationship between crack opening and corrosion penetration is not recommended, due to the different parameters that are able to influence this correlation. Therefore, two fundamental parameters, the ratio of the concrete cover to the rebar diameter and the concrete strength, have also been considered. The considerations made regarding these parameter test results have been rearranged and the result is a formulation that shows reduced scatter
Abstract
The corrosion of reinforcement in concrete is the most common degradation phenomenon of reinforced concrete structures. Reinforced concrete elements subjected to corrosion [...]
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Indicator of carbonation front in concrete as substitute to phenolphthalein
S. Chinchón-Payá, C. Andrade, S. Chinchón-Yepes

Cement and Concrete Research (2016). Vol. 82, pp. 87-91

Abstract
A method to substitute the recognized toxic phenolphthalein in mortars and concretes is proposed. It comprises putting a portland cement sample in contact with an innocuous solution, curcumin-based, which acts as an indicator yielding a red color in areas where there is alkaline reserve (pH ~ 12) and yellow in carbonate zones (pH ≤ 9). Solutions containing curcumin extracted from commercial turmeric powder and from the rhizomes of the turmeric plant were prepared by using ethanol as a solvent. Subsequently it has been experienced with solutions in which curcumin has been used with a purity of over 95%. The dissolution of curcumin can be used with the same reliability as phenolphthalein in the carbonation process with the advantage that it is safe and presents no health risks.
Abstract
A method to substitute the recognized toxic phenolphthalein in mortars and concretes is proposed. It comprises putting a portland cement sample in contact with an innocuous [...]
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Review of the Current State of Knowledge on the Effects of Radiation on Concrete
T. Rosseel, I. Maruyama, Y. Pape, O. Kontani, A. Giorla, I. Remec, J. Wall, M. Sircar, C. Andrade, M. Ordoñez

Journal of Advanced Concrete Technology (2016). Vol. 14 (7), pp. 368-383

Abstract
A review of the current state of knowledge on the effects of radiation on concrete in nuclear power production applications is presented. Emphasis is placed on the effects of radiation damage, as reflected by changes in engineering properties of concrete, in the evaluation of the long-term operation and for plant life or aging management of nuclear power plants (NPPs) in Japan, Spain, and the United States. National issues and concerns are described for Japan and the United States followed by a discussion of the fundamental understanding of the effects of radiation on concrete. Specifically, the effects of temperature, moisture content, and irradiation on ordinary Portland cement paste and the role of temperature and neutron energy spectra on radiation-induced volumetric expansion (RIVE) of aggregate-forming minerals are described. This is followed by a discussion of the bounding conditions for extended operation; the significance of accelerated irradiation conditions; the role of temperature and creep; and how these issues are being incorporated into numerical and meso-scale models. From these insights on radiation damage, analyses of these effects on concrete structures are reviewed, and the current status of work in Japan and the United States is described. Also discussed is the recent formation of a new international scientific and technical organization, the International Committee on Irradiated Concrete, to provide a forum for timely information exchanges among organizations pursuing the identification, quantification, and modeling of the effects of radiation on concrete in commercial nuclear applications. The paper concludes with a discussion of research gaps, including (1) interpreting test-reactor data, (2) evaluating service-irradiated concrete for aging management and to inform radiation damage models with the Zorita NPP (Spain) serving as the first comprehensive test case, (3) irradiated-assisted alkali-silica reactions, and (4) RIVE under constrained conditions.
Abstract
A review of the current state of knowledge on the effects of radiation on concrete in nuclear power production applications is presented. Emphasis is placed on the effects [...]
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Substantial global carbon uptake by cement carbonation
F. Xi, S. Davis, P. Ciais, D. Crawford-Brown, D. Guan, C. Pade, T. Shi, M. Syddall, J. Lv, L. Ji, L. Bing, J. Wang, . Wei, K. Yang, B. Lagerblad, I. Galan, C. Andrade, Y. Zhang, Z. Liu

Nature Geoscience (2016). Vol. 9, pp. 880-883

Abstract
Calcination of carbonate rocks during the manufacture of cement produced 5% of global CO2 emissions from all industrial process and fossil-fuel combustion in 20131,2. Considerable attention has been paid to quantifying these industrial process emissions from cement production2,3, but the natural reversal of the process—carbonation—has received little attention in carbon cycle studies. Here, we use new and existing data on cement materials during cement service life, demolition, and secondary use of concrete waste to estimate regional and global CO2 uptake between 1930 and 2013 using an analytical model describing carbonation chemistry. We find that carbonation of cement materials over their life cycle represents a large and growing net sink of CO2, increasing from 0.10 GtC yr−1 in 1998 to 0.25 GtC yr−1 in 2013. In total, we estimate that a cumulative amount of 4.5 GtC has been sequestered in carbonating cement materials from 1930 to 2013, offsetting 43% of the CO2 emissions from production of cement over the same period, not including emissions associated with fossil use during cement production. We conclude that carbonation of cement products represents a substantial carbon sink that is not currently considered in emissions inventories.
Abstract
Calcination of carbonate rocks during the manufacture of cement produced 5% of global CO2 emissions from all industrial process and fossil-fuel combustion in 20131,2. [...]
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FIBRESHIP project: Engineering, production and life cycle management for the complete construction of large length fibrebased ships.
A. Jurado, C. Garcia, E. Sanchez, P. Beltran

TSI SL's personal collection (2020). 3

Abstract
Fibre-Reinforced Polymer (FRP) materials are widely used in the construction of small-length vessels due to their light weight and high strength to weight ratio. However, the use of FRP materials in vessels above 50 m length is only allowed to secondary structural elements of the vessel. Hence, it is necessary to promote the creation of new regulatory frameworks to permit the construction of large-length vessels using composite laminates in all parts of the vessel structure to enable the development of this interesting technology for the reduction of weight. FIBRESHIP proposes to create a new market focused on the construction of large-length vessels based uniquely on lightweight composites. The results of this project are attracting considerable interest within the shipping industry as the extensive use of FRP materials in large-length vessels induces an important reduction of the weight with respect to the conventional steel ships. This significant weight reduction decreases the vessel bunkering consumption, increases the payload cargo capacity, and avoids the corrosion phenomena in the vessel among other identified benefits.
Abstract
Fibre-Reinforced Polymer (FRP) materials are widely used in the construction of small-length vessels due to their light weight and high strength to weight ratio. However, [...]
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First steps of the FIBRESHIP project: Engineering, production and life cycle management for the complete construction of large length fibre-based ships.
R. Salinas, I. GARCIA, J. García-Espinosa, X. Martinez

TSI SL's personal collection (2020). 2

Abstract
The main objective of the FIBRESHIP project is to enable the building of the complete hull and superstructure of large-length seagoing and inland ships in FRP materials by overcoming few technical challenges. In order to achieve this objective, the project will develop, qualify and audit innovative FRP materials for marine applications, elaborate new design and production guidelines and procedures, generate efficient production and inspection methodologies, and develop new validated software analysis tools. Clear performance indicators will be designed and applied in the evaluation of the different solutions developed for three targeted vessels categories. Finally, the different technologies generated in FIBRESHIP will be first validated and then demonstrated by using advanced simulation techniques and experimental testing on real-scale structures. This paper is dealing with the presentation of the project scope and progress of the FIBRESHIP project over the first six months.
Abstract
The main objective of the FIBRESHIP project is to enable the building of the complete hull and superstructure of large-length seagoing and inland ships in FRP materials by [...]
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FIBRESHIP, the greatest challenge of using composite materials for the construction of large-length ships
A. Jurado, . C.Garcia, . E.Sanchez

TSI SL's personal collection (2020). 1

Abstract
FIBRESHIP (H2020, Grant 723360) is an ambitious innovation project funded by the European Commission, which is participated by 18 European partners led by the Spanish company TSI. The main objective of FIBRESHIP is to overcome the great technical challenge of replacing the metallic materials currently used for the construction of large-lenght vessels for composite materials. To carry out this task, this project is addressed from different points of view: i) shipping market and bussiness analysis of composite vessels, ii) analysis and numerical modeling of the materials selected, iii) development of the structural design using a finite element analysis software, and, iv) analysis of the construction and assembly procedures, structural health monitoring techniques, and ship life cycle. The study and implementation of this technology for the construction of large-length composite vessels is carried out through the design of three types of vessels over 50 meters, which are considered as the most promising in the market: a container ship of 245 meters length, a ROPAX of 185 meters and a special service oceanographic vessel of 80 meters. In addition, specific numerical models are being developed and validated through experimental testing campaigns. Eventually, different structural health monitoring strategies and production models adapted to this technology.
Abstract
FIBRESHIP (H2020, Grant 723360) is an ambitious innovation project funded by the European Commission, which is participated by 18 European partners led by the Spanish [...]
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Materials for large length fibre-based ships. Characterization, selection, and numerical analysis
J. Jurado Granados

Open Access Repository of the FIBRESHIP project (2020). 6

Abstract
Fourth dissemination action for university students for increasing the interest in the use of fibre-reinforced polymers for large-length vessels design and shipbuilding in the future naval architects and marine engineers. This presentation was held at the School of Naval Architecture and Ocean Engineering (ETSINO) of the Technical University of Madrid on the 1st of October of 2019. In this presentation, the process of materials selection for marine applicactions and the numerical models for characterizing and predicting the fatigue and failure of such materials were introduced.
Abstract
Fourth dissemination action for university students for increasing the interest in the use of fibre-reinforced polymers for large-length vessels design and shipbuilding in [...]
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Numerical tools for the design of fibre-based ships of large lengths
J. Jurado Granados

Open Access Repository of the FIBRESHIP project (2020). 4

Abstract
First dissemination action for university students at the School of Naval and Ocean Engineering (ETSINO) of Cartagena University (UPCT) with the intention of increasing the interest of the students and future engineers and naval architects in the use of composite materials for the design and shipbuilding of large-length vessels. In this presentation, the numerical models developed for predicting the fatigue and failure of composite materials were showed. Besides, the new numerical tools to design and anayze fiber-based ships of large length were introduced, specifically a coupled seakeeping-FEA tool, a new graphical user interface (GUI) for materials definition, hull girder analysis and collapse assesemt.
Abstract
First dissemination action for university students at the School of Naval and Ocean Engineering (ETSINO) of Cartagena University (UPCT) with the intention of increasing the [...]
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Future trends in research on reinforcement corrosion
C. Andrade

(2016). Corrosion of Steel in Concrete Structures, pp.269-288

Abstract
The concept of service life in the science in reinforcement corrosion has evolved from a basic description of phenomena to a more detailed engineering perspective in which quantification of processes is of vital importance. This chapter treats the following subjects: (1) causes of reinforcement corrosion – carbonation, chloride ingress and stress corrosion cracking, (2) corrosion onset and chloride threshold, (3) corrosion propagation period, (4) modelling of service life, (5) additional preventive methods, (6) repair materials and techniques and (7) corrosion measurement techniques. The paper does not develop the known aspects of these different subjects, but rather identifies those aspects still needing further research work. In this exercise, the modelling of processes and their incorporation into structural and engineering calculations is identified as the most important subject needing to be improved and further developed in the near future.
Abstract
The concept of service life in the science in reinforcement corrosion has evolved from a basic description of phenomena to a more detailed engineering perspective [...]
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Corrosion induced cracking: Effect of different corrosion rates on crack width evolution
F. Pedrosa, C. Andrade

Construction and Building Materials (2017). Vol. 133, pp. 525-533

Abstract
Reinforcement corrosion leads to several damage types that influence the structure service lifetime, among which can be mentioned the cracking of concrete cover due to the increase in volume of the oxides with respect to the original volume of the parent steel. The relation between crack width and corrosion level has been studied by some authors while its analytical or numerical modelling is attracting increasing interest. In the modelling attempts, it has not been found the consideration of the corrosion rate effect, which, on the other hand was experimentally demonstrated more than 20 years ago. In the present paper the impact of different corrosion rates on the crack width development of reinforced concrete (RC) was studied. Identical RC prisms were subjected to accelerated corrosion in galvanostatic conditions with distinct electrical currents each, in order to monitor the superficial crack width growth of every specimen. Crack width growth with steel attack penetration is analysed as a two stage bilinear process where the crack width grows faster in the first stage. An empirical relation is found between the ratio crack width/steel attack and the corrosion rate applied for the first stage of cracking. With the new-found relation, a formula relating crack width evolution through time with the corrosion rate is presented. This study shows that it is crucial to take into account the strong influence of the corrosion rate on the crack width/steel attack ratio variation in order to successfully predict corrosion induced cracking
Abstract
Reinforcement corrosion leads to several damage types that influence the structure service lifetime, among which can be mentioned the cracking of concrete cover due to the [...]
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Contactless safety evaluation of damaged structures through energetic criteria
L. Saucedo-Mora, C. Andrade, C. López, J. Sánchez, A. Zamora

Structural Control and Health Monitoring (2017). Vol. 25 (1), pp. 1-11

Abstract
The reinforced concrete structures need to be monitored to ensure their structural integrity, but sometimes those measurements are very local, and the instrument is complex to locate physically in the structure and may interfere on it. Digital Image Correlation is a noncontact and nondestructive experimental technique capable to measure the displacement field in a big region of a structure with a great accuracy. This allows extracting valuable information from the fracture processes of reinforced concrete structures, critical for the evaluation of the structural integrity. The measurement of the energy dissipated by the structure is essential for the identification of the strength mechanisms that are failing in the structure and to identify a proper repair. Also, using fracture mechanics, other valuable information are extracted from the fracture processes of the reinforced concrete beam, such as the Modes I and II fracture energy released at each loading step, which is essential to evaluate the elastic energy that the structure can accumulate before collapse. The examples enable to anticipate the importance of Digital Image Correlation for future large scale studies of fracture in concrete and other materials related to construction.
Abstract
The reinforced concrete structures need to be monitored to ensure their structural integrity, but sometimes those measurements are very local, and the instrument is complex [...]
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Corrosion-induced brittle failure in reinforcing steel
J. Sánchez, J. Fullea, C. Andrade

Theoretical and Applied Fracture Mechanics (2017). Vol. 92, pp. 229-232

Abstract
Steel rebar corrosion is the main cause of reinforced concrete structure deterioration and shortened service life. A number of corrosion mechanisms induce geometric flaws in rebar, reducing its mechanical strength. Interstitial hydrogen, which lowers steel toughness, may also prompt embrittlement.This paper discusses the effect of local, pitting and corrosion stress on steel rebar performance. The findings show that rebar bearing strength depends on corrosion morphology and weight loss, which would explain the scatter in experimental results when the latter is the sole parameter studied.
Abstract
Steel rebar corrosion is the main cause of reinforced concrete structure deterioration and shortened service life. A number of corrosion mechanisms induce geometric flaws [...]
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The effect of two types of modified Mg-Al hydrotalcites on reinforcement corrosion in cement mortar
Z. Yang, R. Polder, J. Col, C. Andrade

Cement and Concrete Research (2017). Vol. 100, pp. 186-202

Abstract
Two modified Mg-Al hydrotalcites (MHTs), (MHT-pAB and MHT-NO2) were incorporated into mortar (with different w/c ratios) in two different ways: (1) as one of the mixing components in bulk mortar; (2) as part of cement paste coating of the reinforcing steel. Accelerated chloride migration, cyclic wetting-drying and diffusion tests were performed to investigate their effect on reinforcement corrosion. The results indicated that MHTs could be promising alternatives for preventing chloride-induced corrosion when an appropriate dosage is adopted and applied in a proper way, particularly, replacing 5% mass of cement by MHT-pAB in bulk mortar or as a coating of reinforcing steel (MHT-pAB/MHT-NO2 to replace 20% mass of cement). The effect of MHT-pAB on time-to-corrosion initiation (TTC) of reinforcing steel was estimated using the DuraCrete model. It was found that the incorporation of 5% MHT-pAB in bulk mortar led to a more than double TTC relative to reference mortar without MHTs.
Abstract
Two modified Mg-Al hydrotalcites (MHTs), (MHT-pAB and MHT-NO2) were incorporated into mortar (with different w/c ratios) in two different ways: (1) as one of the [...]
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Reliability analysis of corrosion onset: initiation limit state
C. Andrade

Journal of Structural Integrity and Maintenance (2017). Vol. 2 (4), pp. 200-208

Abstract
The relatively premature failure of structures by steel corrosion has increased interest in incorporating to the standards calculation of the time to corrosion. These models in general identify the end of service life with the starting of bar corrosion, either by chlorides or by carbonation. Additionally, from the publications of the project Duracrete, funded by the EU, probabilistic treatments have been applied to steel depassivation which is associated with a serviceability limit state (SLS). Thus, fib Model Code (MC2010) recommends a probability of failure of 10% for calculation of the time to corrosion. However, this recommendation leads to uncertainties because, on the one hand, the chloride threshold is not a fixed value and the carbonation front affects first the external face of the bar, developing progressive perimetral damage and, on the other hand, the consideration of the limit state as an SLS, with so low a fixed failure probability, introduces some degree of contradiction with the classical definition of the SLS. This is because, while the SLS is defined as a failure to fulfil the design prescriptions, any structural design performance changes just at the moment of steel depassivation. Additionally, no treatment on how to consider the damaged section or corrosion propagation model is usually given in the MC2010 or other standard and how to verify the classical SLS and ultimate limit state (ULS) is undefined. The present work introduces new perspectives on the subject from a probabilistic point of view by, (1) treating statistically the depassivation step, (2) by introducing a corrosion propagation model and quantifying the corrosion limit states and (3) by calculation of the depassivation probability which is dependent on the rate of the deterioration process itself. The whole exercise stresses the need to not consider a fixed value (10%) associated with a SLS as the probability of corrosion, but to consider it a limit state of “corrosion initiation” following ISO 2394. The value of the adequate probability of corrosion would be dependent on the consequences of the failure and on the rates of chloride ingress, of carbonation or of steel corrosion.
Abstract
The relatively premature failure of structures by steel corrosion has increased interest in incorporating to the standards calculation of the time to corrosion. These models [...]
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Fracto-surface mobility mechanism in high-strength steel wires
J. Sánchez, J. Fullea, C. Andrade

Engineering Fracture Mechanics (2017). Vol. 186, pp. 410-422

Abstract
Stress corrosion cracking, a mechanism governing steel deterioration, has yet to be fully understood. This article introduces a supplement to the surface mobility mechanism proposed by Galvele to include fracture mechanics principles. In the model proposed, anodic dissolution is regarded as the source of vacancies that would be driven by a stress gradient to the crack tip under non-stationary conditions. Denominated the fracto-surface mobility mechanism (FSMM), it explains material mechanical failure based on vacancy diffusion across the metal surface.
Abstract
Stress corrosion cracking, a mechanism governing steel deterioration, has yet to be fully understood. This article introduces a supplement to the surface mobility mechanism [...]
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Design and evaluation of service life through concrete electrical resistivity
C. Andrade

ALCONPAT (2018). Vol. 8 (3), pp. 264-279

Abstract
This paper describes the use of concrete electrical resistivity as durability performance parameter and the complementary information that resistivity can provide like: setting period, mechanical strength and degree of curing. Also, it is explained how to design the concrete mix to obtain a target resistivity. Current codes have prescriptive requirements for the durability of concrete and reinforcement corrosion. However, modern trends specify the performance rather than the concrete characteristics. This performance approach demands to define a durability controlling parameter, such as the chloride diffusion coefficient, with its corresponding test and the model to predict the time to steel corrosion.
Abstract
This paper describes the use of concrete electrical resistivity as durability performance parameter and the complementary information that resistivity can provide like: setting [...]
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Brief historical notes
C. Andrade

ALCONPAT (2018). Vol. 8 (3), pp. I-V

Abstract
Anniversaries are a good excuse to make some summaries of historical events. Very briefly, some advances made from the initial research in the speciality of reinforcement corrosion which started in the 60’s are summarized. The use of electrochemical techniques was a milestone which enabled, from the decade of the 1970, to study the effect of each variable with much more rigour. The studies on service life started in the decade of 1980, although they were not of general interest until the next decade. From 1990 RILEM Committees and the Iberoamerican Program on Corrosion of CYTED extended the knowledge so widely that in the XXI century the subject attracts much research interest.
Abstract
Anniversaries are a good excuse to make some summaries of historical events. Very briefly, some advances made from the initial research in the speciality of reinforcement [...]
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Model Predictive Control applied to thermostatic controlled systems
F. Lazzari, G. Mor Martinez, J. Cipriano, E. Gabaldon, S. Danov, B. Grillone

Florencia Lazzari's personal collection (2020). 1

Abstract
A Model Predictive Control (MPC) was developed to optimize the performance of a residential heat pump. To test the MPC, the real system was replaced by a Modelica emulator of the entire house. The building’s thermal behavior model was developed as an Auto-Regressive linear model with eXogenous variables (ARX) and the optimization algorithm was based in a genetic algorithm. The proposed predictive model to characterize the building’s thermal behavior was developed successfully. And the MPC is already implemented and validated, but the total integration with the emulator of the system and the feedback loop has not been yet assembled. In this way, we are looking towards to end this task and complete the further analysis.
Abstract
A Model Predictive Control (MPC) was developed to optimize the performance of a residential heat pump. To test the MPC, the real system was replaced by a Modelica emulator [...]
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Apparent diffusion coefficient of oxygen and corrosion control of reinforcement rebar coated with primers
E. Pazini, C. Andrade

ALCONPAT (2018). Vol. 8 (3), pp. 288-301

Abstract
The present work evaluates the influence of five different types of coatings applied on the rebar on apparent diffusion coefficient of oxygen (Dap (O2)) and on the corrosion intensity (Icorr) in comparison with a reference coating composed of a cement-sand mortar. Oxygen flow (J (O2)) until the rebar was measured by potenciostático method in the steady state and the corrosion intensity (Icorr) was monitored by the Polarization Resistance technique (Rp). Evaluations for porosity of coatings were made through magnifying glasses, optical microscopy and SEM. The primers that represent barrier protection systems were, under the conditions tested, less permeable to oxygen. The apparent diffusion coefficient values (Dap (O2)) ranged from 2.1 x 10-6 cm2/s to 4 x 10-9 cm2/s, causing variations in the corrosion intensity measurements (Icorr), due to the cathodic corrosion process control.
Abstract
The present work evaluates the influence of five different types of coatings applied on the rebar on apparent diffusion coefficient of oxygen (Dap (O2)) and on the corrosion [...]
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Corrigendum to “Threshold concentration of chlorides in concrete for stainless steel reinforcement: Classic austenitic and new duplex stainless steel”
A. Panchón-Montaño, J. Sánchez, C. Andrade, J. Fullea, E. Moreno, V. Matres

Construction and Building Materials (2018). Vol. 189, p. 1303

Abstract
The authors regret that Equation 1: 30%w Ni not is correct. Should be changed to 30%w N, so that is; PREn = %w Cr + 3.3%w Mo + 30%w N-%w Mn. Footnote in Fig. 5 is not correct. Should be changed to “Micrographs (4×) of EN 1.4362/2304 duplex rebar; left: after removal from specimen; right: after pickling (4×)”. The authors would like to apologise for any inconvenience caused
Abstract
The authors regret that Equation 1: 30%w Ni not is correct. Should be changed to 30%w N, so that is; PREn = %w Cr + 3.3%w Mo + 30%w N-%w Mn. Footnote in [...]
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Threshold concentration of chlorides in concrete for stainless steel reinforcement: Classic austenitic and new duplex stainless steel
A. Panchón-Montaño, J. Sánchez, C. Andrade, J. Fullea, E. Moreno, V. Matres

Construction and Building Materials (2018). Vol. 186, pp. 495-502

Abstract
Stainless steel rebars is used to lengthen the service life of structures in aggressive media. Corrosion resistance was studied in five grades of mortar-embedded stainless steel: EN 1.4307, EN 1.4404, EN 1.4482, EN 1.4362 and EN 1.4462. A modified accelerated chloride attack was applied to prevent steel rebar polarisation and artificial re-passivation. The critical chloride concentration was determined. Based on corrosion rate, service life was calculated for a given exposure at two probability levels.
Abstract
Stainless steel rebars is used to lengthen the service life of structures in aggressive media. Corrosion resistance was studied in five grades of mortar-embedded stainless [...]
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Updating Carbon Storage Capacity of Spanish Cements
C. Andrade, M. Sanjuán

Sustainability (2018). Vol. 10 (12), pp. 1-15

Abstract
The fabrication of cement clinker releases CO2 due to the calcination of the limestone used as raw material, which contributes to the greenhouse effect. The industry is involved in a process of reducing this amount liberated to the atmosphere by mainly lowering the amount of clinker in the cements. The cement-based materials, such as concrete and mortars, combine part of this CO2 by a process called “carbonation”. Carbonation has been studied lately mainly due to the fact that it induces the corrosion of steel reinforcement when bringing the CO2 front to the surface of the reinforcing bars. Thus, the “rate of carbonation” of the concrete cover is characterized by and linked to the length of service life of concrete structures. The studies on how much CO2 is fixed by the hydrated phases are scarce and even less has been studied the influence of the type of cement. In present work, 15 cements were used to fabricate paste and concrete specimens withwater/cement (w/c) ratios of 0.6 and 0.45 which reproduce typical concretes for buildings and infrastructures. The amount of carbon dioxide uptake was measured through thermal gravimetry. The degree of carbonation, (DoC) is defined as the CO2 fixed with respect to the total theoretical maximum and the carbon storage capacity (CSC) as the carbonation uptake by a concrete element, a family or the whole inventory of a region or country. The results in the pastes where analyzed with respect to the uptake by concretes and indicated that: (a) the humidity of the pores is a critical parameter that favours the carbonation reaction as higher is the humidity (within the normal atmospheric values), (b) all types of cement uptake CO2 in function of the CaO of the clinker except the binders having slags, which can uptake additional CO2 giving aDoC near or above 100%. The CSC of Spain has been updated with respect to a previous publication resulting in proportions of 10.8–11.2% of the calcination emissions, through considering a ratio of “surface exposed/volume of the element” of 3 as an average of the whole Spanish asset of building and infrastructures.
Abstract
The fabrication of cement clinker releases CO2 due to the calcination of the limestone used as raw material, which contributes to the greenhouse effect. The industry [...]
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Advances in Characterization of Gas Transport in Concrete: Determination of Oxygen Diffusion Coefficient from Permeability Coefficient and Porosity
P. Linares, C. Andrade, D. Baza

(2018). Service Life and Durability of Reinforced Concrete Structures. RILEM Bookseries, Vol 17, pp. 87-97. Springer, Cham

Abstract
One of the most relevant mechanisms that influence the life service of concrete (carbonation, compactness, alkaline protection) is gas diffusion through its mass. However, determination of gas diffusion coefficient in concrete is not a simple task. There is not a general standard which determines the test procedure. Other approaches or alternative parameters could be used in order to obtain the gas diffusion coefficient, including the use of permeability coefficient. Both parameters are dependent on material porosity and moisture content. The literature already proposes generic correlations for these parameters, but these correlations do not support the direct derivation of the gas diffusion coefficient. This paper presents the results of research carried out to analyse these generic correlations and to propose specific expressions that support the derivation of a value for the oxygen diffusion coefficient, based on the porosity and permeability coefficients. The research was centred on a experimentation process to obtain these parameters. A diffusion chamber was designed and built for use with two types of concrete mix, two distinct concrete curing processes and three separate values for humidity. Each test case sought to derive values for oxygen diffusion and permeability coefficients.
Abstract
One of the most relevant mechanisms that influence the life service of concrete (carbonation, compactness, alkaline protection) is gas diffusion through its mass. However, [...]
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Propagation of reinforcement corrosion: principles, testing and modelling
C. Andrade

Materials and Structures (2018). Vol. 52 (2), pp. 1-26

Abstract
Reinforcement corrosion is the risk most frequently cited to justify concrete durability research. The number of studies specifically devoted to corrosion propagation, once the object of most specialised papers, has declined substantially in recent years, whilst the number addressing initiation, particularly where induced by chlorides, has risen sharply. This article briefly describes the characteristics of steel corrosion in concrete that need to be stressed to dispel certain misconceptions, such as the belief that the corrosion zone is a pure anode. That is in fact seldom the case and as the zone is also affected by microcells, galvanic corrosion accounts for only a fraction of the corrosion rate. The role of oxygen in initiating corrosion, the scant amount required and why corrosion can progress in its absence are also discussed. Another feature addressed is the dependence of the chloride threshold on medium pH and the buffering capacity of the cement, since corrosion begins with acidification. Those general notions are followed by a review of the techniques for measuring corrosion, in particular polarisation resistance, which has proved to be imperative for establishing the processes involved. The inability to ascertain the area affected when an electrical signal is applied to large-scale elements is described, along with the concomitant need to use a guard ring to confine the current or deploy the potential attenuation method. The reason that measurement with contactless inductive techniques is not yet possible (because the area affected cannot be determined) is discussed. The method for integrating corrosion rate over time to find cumulative corrosion, Pcorr, is explained, together with its use to formulate the mathematical expressions for the propagation period. The article concludes with three examples of how to use corrosion rate to assess cathodic protection, new low-clinker cements or determine the chloride threshold with an integral accelerated service life method
Abstract
Reinforcement corrosion is the risk most frequently cited to justify concrete durability research. The number of studies specifically devoted to corrosion propagation, once [...]
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Concrete Structures: On-site electrochemical techniques and concrete resistivity to predict service life Part 1 - Corrosion measurement techniques
C. Andrade

Ochrona przed Korozją (2019). Vol. 1 (4)

Abstract
Concrete protects the steel of the reinforcements in a similar manner than do the paints but with the particularity that it is a material chemically active and evolving for decades. Concrete provides a very alkaline electrolyte encapsulated in its pore network. The steel may remain passive indefinitely but chlorides and atmospheric carbon dioxide penetrate the pores and reaching the reinforcement promote corrosion, which impairs the concrete structural properties inducing the cover cracking and the loss in steel-concrete bond. Calculation of service life is becoming an important subject in engineering terms due to the increasing demand to produce buildings and infrastructures with service life beyond 100 years. In the paper focus will be devoted to two main areas: 1) the measurement techniques in concrete and permanent probes, including on site methods for large structures and contactless (inductive) methods 2) the illustration of the corrosion resistance control exerted by concrete resistivity which enables the calculation of the diffusion of ions through the concrete and the prediction of the corrosion rate in function of the climatic conditions
Abstract
Concrete protects the steel of the reinforcements in a similar manner than do the paints but with the particularity that it is a material chemically active and evolving for [...]
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Concrete structures: on-site electrochemical techniques and concrete resistivity to predict service life Part 2: Service life of structural concrete, present and future challenges
C. Andrade

Ochrona przed Korozją (2019). Vol. 2019 (2)

Abstract
Concrete protects the steel of the reinforcements in a similar manner than do the paints but with the particularity that it is a material chemically active and evolving for decades. Concrete provides a very alkaline electrolyte encapsulated in its pore network. The steel may remain passive indefinitely but chlorides and atmospheric carbon dioxide penetrate the pores and reaching the reinforcement promote corrosion, which impairs the concrete structural properties inducing the cover cracking and the loss in steel-concrete bond. Calculation of service life is becoming an important subject in engineering terms due to the increasing demand to produce buildings and infrastructures with service life beyond 100 years. In the paper focus will be devoted to two main areas: 1) the measurement techniques in concrete and permanent probes, including on site methods for large structures and contactless (inductive) methods 2) the illustration of the corrosion resistance control exerted by concrete resistivity which enables the calculation of the diffusion of ions through the concrete and the prediction of the corrosion rate in function of the climatic conditions.
Abstract
Concrete protects the steel of the reinforcements in a similar manner than do the paints but with the particularity that it is a material chemically active and evolving for [...]
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Numerical Simulation of Fatigue in Composites
J. Jurado Granados, X. Martinez, D. Di Capua, L. Barbu

Presentations at Congresses and Seminars (2018). 1

Abstract
For the past several years, composite marine structures have been designed but without having a complete characterization the composite materials. The main reason is due to the large quantity of variables that affect the behavior of said materials. One of the tasks that has not been properly characterized is the behavior of composite structures under fatigue loads that appear in marine structures that are subjected to cyclic loads. Therefore, numerical tools that characterize fatigue performance are required in order to design more reliable structures. The formulation proposed in this work is based on the Serial/Parallel Rule of Mixtures [1] and a fatigue damage model [2]. The Serial/Parallel Rule of Mixtures can be understood as a constitutive law manager that provides the response of the composite from the constitutive performance of its constituents. Therefore, the constitutive laws chosen to represent the behavior of each constituent material have to fit with their real performance. Also, the fatigue damage model is based on the use of a reduction function which takes into account the cyclic degradation of the materials, both strength and stiffness degradation, in function of the number of cycles, maximum stress and stress amplitude. Current work presents a numerical tool developed to characterize fatigue in composites. The fatigue behavior of constituent materials is defined using mechanic parameters taken from literature. Afterwards, a reproduction of the tests will be done in order to validate the fatigue formulation proposed. [1] Car, E., Oller, S., Oñate, E. "Estudio del comportamiento no lineal en materiales compuestos", Techincal Report 264,CIMNE, 1997. [2] Oller, Salomon, O., Oñate, E. “A continuum mechanics model for mechanical fatigue analysis", Composite Materials Science, Vol 32, Issue 2, pp 175-195, 2005.
Abstract
For the past several years, composite marine structures have been designed but without having a complete characterization the composite materials. The main reason is due to [...]
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Porosity and electrical resistivity-based empirical calculation of the oxygen diffusion coefficient in concrete
P. Linares-Alemparte, C. Andrade, D. Baza

Construction and Building Materials (2019). Vol. 198, pp. 710-717

Abstract
Concrete carbonation induced by gas transport has an adverse effect on the service life of the steel-reinforced material. Gas tightness is crucial where concrete is used to contain radioactive materials and of utmost importance where acting as a radon barrier. Since as a rule gas travel inside concrete is governed either by diffusion or permeability, the material’s performance in that respect is assessed by analysing those two parameters. The gas diffusion coefficient in concrete is not readily found, however, due to the practical difficulties involved in preventing gas from leaking out of standard diffusion cells. An alternative approach is to measure permeability at high gas concentration and pressure. The existence of a relationship between the oxygen diffusion coefficient and permeability in OPC concrete was established by the authors in a previous paper. Diffusion has also been shown to be related to porosity and, in solutions, to electrical resistivity. Little is known, however, about the relationship between gas diffusion and resistivity where the pores may be filled not with a liquid, but with air. Inasmuch as resistivity is a non-destructive technique and porosity a property that can be readily measured, these two parameters could be used to directly assess concrete durability, its performance in nuclear facilities and its suitability as a radon barrier. This paper describes a study conducted to formulate equations from which to analytically determine the oxygen diffusion coefficient. These equations are derived from empirical measurements of oxygen diffusion coefficient, concrete porosity and electrical resistivity. The findings, which corroborate the existence of such relationships, were used to formulate an equation to calculate the diffusion coefficient directly from the experimental values of concrete porosity and resistivity. Since porosity depends primarily on concrete batching, curing and moisture content, two OPC concrete mixes were prepared using different water/cement ratios and two curing conditions. The combination resulted in four types of concrete. Pre-conditioning at three values of relative humidity was subsequently deployed.
Abstract
Concrete carbonation induced by gas transport has an adverse effect on the service life of the steel-reinforced material. Gas tightness is crucial where concrete [...]
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Numerical and experimental procedure for material calibration using the serial/parallel mixing theory, to analyze different composite failure modes
J. Jurado Granados, X. Martinez, N. Nash, C. Bachour, . Ioannis, A. Comer, D. Di Capua

Joel Jurado's journal papers (2019). 1

Abstract
This work proposes a calibration procedure to obtain the material parameters required by the Serial/Parallel Mixing Theory for the analysis of composites. A set of experimental tests are defined to obtain the main composite failure modes. Then, it is proposed to calculate the parameters required by the formulation using the experimental results. The procedure proposed is validated by comparing the numerical results, with those obtained from the experimental campaign. This comparison shows that the Serial/Parallel mixing theory is capable of representing the failure modes of the composite for different loading scenarios as well as the material toughness.
Abstract
This work proposes a calibration procedure to obtain the material parameters required by the Serial/Parallel Mixing Theory for the analysis of composites. A set of experimental [...]
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High performance reduced order modeling techniques based on optimal energy quadrature: application to geometrically non-linear multiscale inelastic material modeling
M. Caicedo, J. Mroginski, S. Toro, M. Raschi, A. Huespe, J. Oliver

Archives of Computational Methods in Engineering (2019). Vol. 26 (4), pp. 771-192 (Preprint)

Abstract
A High-Performance Reduced-Order Model (HPROM) technique, previously presented by the authors in the context of hierarchical multiscale models for non linear-materials undergoing infinitesimal strains, is generalized to deal with large deformation elasto-plastic problems. The proposed HPROM technique uses a Proper Orthogonal Decomposition procedure to build a reduced basis of the primary kinematical variable of the micro-scale problem, defined in terms of the micro-deformation gradient fluctuations. Then a Galerkin-projection, onto this reduced basis, is utilized to reduce the dimensionality of the micro-force balance equation, the stress homogenization equation and the effective macro-constitutive tangent tensor equation. Finally, a reduced goal-oriented quadrature rule is introduced to compute the non-affine terms of these equations. Main importance in this paper is given to the numerical assessment of the developed HPROM technique. The numerical experiments are performed on a micro-cell simulating a randomly distributed set of elastic inclusions embedded into an elasto-plastic matrix. This micro-structure is representative of a typical ductile metallic alloy. The HPROM technique applied to this type of problem displays high computational speed-ups, increasing with the complexity of the finite element model. From these results, we conclude that the proposed HPROM technique is an effective computational tool for modeling, with very large speed-ups and acceptable accuracy levels with respect to the high-fidelity case, the multiscale behavior of heterogeneous materials subjected to large deformations involving two well-separated scales of length.
Abstract
A High-Performance Reduced-Order Model (HPROM) technique, previously presented by the authors in the context of hierarchical multiscale models for non linear-materials undergoing [...]
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Implicit–explicit integration of gradient-enhanced damage models
T. Titscher, J. Oliver, J. Unger

Journal of engineering mechanics (2019). Vol. 145 (7), pp. 1-13 (Preprint)

Abstract
Quasi-brittle materials exhibit strain softening. Their modeling requires regularized constitutive formulations to avoid instabilities on the material level. A commonly used model is the implicit gradient-enhanced damage model. For complex geometries, it still shows structural instabilities when integrated with classical backward Euler schemes. An alternative is the implicit–explicit (IMPL-EX) integration scheme. It consists of the extrapolation of internal variables followed by an implicit calculation of the solution fields. The solution procedure for the nonlinear gradient-enhanced damage model is thus transformed into a sequence of problems that are algorithmically linear in every time step. Therefore, they require one single Newton–Raphson iteration per time step to converge. This provides both additional robustness and computational acceleration. The introduced extrapolation error is controlled by adaptive time-stepping schemes. This paper introduced and assessed two novel classes of error control schemes that provide further performance improvements. In a three-dimensional compression test for a mesoscale model of concrete, the presented scheme was about 40 times faster than an adaptive backward Euler time integration.
Abstract
Quasi-brittle materials exhibit strain softening. Their modeling requires regularized constitutive formulations to avoid instabilities on the material level. A commonly used [...]
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Preface: Computational multiscale modelling and design of new engineering materials
T. Burczynski, J. Oliver, M. Pietrzyk, A. Huespe

International Journal for Multiscale Computational Engineering (2019). Vol. 17 (3), pp. V-VI
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Making use of symmetries in the three-dimensional elastic inverse homogenization problem
C. Méndez, J. Podestá, S. Toro, A. Huespe, J. Oliver

International Journal for Multiscale Computational Engineering (2019). Vol. 17 (3), pp. 261-280

Abstract
The objective of this paper is the design of three-dimensional elastic metamaterials with periodic microarchitectures. The microarchitectures of these materials are attained by following an inverse design technique jointly with an homogenization-based topology optimization algorithm. In this context, we have particularly studied the connection between the symmetry of the material layout at the microscale of 3D periodic composites and the symmetry of the effective elastic properties.We have analyzed some possible Bravais lattices and space groups, which are typically associated with crystallography, to study the way in which the symmetries of these geometrical objects can be usefully used for the microarchitecture design of 3D elastic metamaterial. Following a previous work of the authors for two-dimensional problems, we suggest adopting the design domain of the topology optimization problem coincident with the Wigner-Seitz cells of specific Bravais lattices having the same point group to that of the target elasticity tensor. The numerical assessment described in this paper aims at the design of an extreme material. The solutions obtained with this procedure show that different composite microarchitectures emerge depending on the cell shape selection.
Abstract
The objective of this paper is the design of three-dimensional elastic metamaterials with periodic microarchitectures. The microarchitectures of these materials are attained [...]
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Effect of Environmental Conditioning on the Properties of Thermosetting and Thermoplastic-Matrix Composite Materials by Resin Infusion for Marine Applications (PREPRINT)
N. Nash, A. Portela, C. Bachour, I. Manolakis, A. Comer, A. Comer

Composites Part B: Engineering (2019). Composites Part B 177 (2019) 107271

Abstract
Glass-fibre reinforced polymer (GFRP) laminates were manufactured using Vacuum assisted Resin Transfer Moulding (VaRTM) with a range of thermosetting resins and a novel infusible thermoplastic resin as part of a comprehensive down-selection to identify suitable commercially available resin systems for the manufacture of marine vessels greater than 50 m in length. The effect of immersion in deionised water and in an organic liquid (diesel) on the interlaminar shear strength (ILSS) and glass transition temperature (Tg) was determined. The thermoplastic had the highest Tg of all materials tested and comparable ILSS properties to the epoxy. Immersion in water, however, caused larger reductions in ILSS properties of the thermoplastic compared to the other systems. SEM showed a transition from matrix-dominated failure in the dry condition to failure at the fibre-matrix interface in the wet and organic-wet specimens. The overall performance of the infusible thermoplastic is good when compared to well-established marine resin systems; however, the environmental performance could be improved if the thermoplastic resin is used in conjunction with a fibre sizing that is tailored for use with acrylic-based resin systems.
Abstract
Glass-fibre reinforced polymer (GFRP) laminates were manufactured using Vacuum assisted Resin Transfer Moulding (VaRTM) with a range of thermosetting resins and a novel infusible [...]
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Material design of elastic structures using Voronoi cells
J. Podestá, C. Méndez, S. Toro, A. Huespe, J. Oliver

International Journal for Numerical Methods in Engineering (2018). Vol. 115 (3), pp. 269-292 (Preprint)

Abstract
New tools for the design of metamaterials with periodic microarchitectures are presented. Initially, a two‐scale material design approach is adopted. At the structure scale, the material effective properties and their spatial distribution are obtained through a Free Material Optimization technique. At the microstructure scale, the material microarchitecture is designed by appealing to a Topology Optimization Problem (TOP). The TOP is based on the topological derivative and the level set function. The new proposed tools are used to facilitate the search of the optimal microarchitecture configuration. They consist of the following: (i) a procedure to choose an adequate shape of the unit cell domain where the TOP is formulated and shapes of Voronoi cells associated with Bravais lattices are adopted and (ii) a procedure to choose an initial material distribution within the Voronoi cell being utilized as the initial configuration for the iterative TOP.
Abstract
New tools for the design of metamaterials with periodic microarchitectures are presented. Initially, a two‐scale material design approach is adopted. At the structure scale, [...]
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Reduced order modeling strategies for computational multiscale fracture
J. Oliver, M. Caicedo, A. Huespe, J. Hernández, E. Roubin

Computer Methods in Applied Mechanics and Engineering (2017). Vol. 313, pp. 560-595 (Preprint)

Abstract
The paper proposes some new computational strategies for affordably solving multiscale fracture problems through a FE2 approach. To take into account the mechanical effects induced by fracture at the microstructure level the Representative Volume Element (RVE), assumed constituted by an elastic matrix and inclusions, is endowed with a large set of cohesive softening bands providing a good representation of the possible microstructure crack paths. The RVE response is then homogenized in accordance with a model previously developed by the authors and upscaled to the macro-scale level as a continuum stress–strain constitutive equation, which is then used in a conventional framework of a finite element modeling of propagating fracture. For reduced order modeling (ROM) purposes, the RVE boundary value problem is first formulated in displacement fluctuations and used, via the Proper Orthogonal Decomposition (POD), to find a low-dimension space for solving the reduced problem. A domain separation strategy is proposed as a first technique for model order reduction: unconventionally, the low-dimension space is spanned by a basis in terms of fluctuating strains, as primitive kinematic variables, instead of the conventional formulation in terms of displacement fluctuations. The RVE spatial domain is then decomposed into a regular domain (made of the matrix and the inclusions) and a singular domain (constituted by cohesive bands), the required RVE boundary conditions are rephrased in terms of strains and imposed via Lagrange multipliers in the corresponding variational problem. Specific low-dimensional strain basis is then derived, independently for each domain, via the POD of the corresponding strain snapshots. Next step consists of developing a hyper-reduced model (HPROM). It is based on a second proposed technique, the Reduced Optimal Quadrature (ROQ) which, again unconventionally, is determined through optimization of the numerical integration of the primitive saddle-point problem arising from the RVE problem, rather than its derived variational equations, and substitutes the conventional Gauss quadrature. The ROQ utilizes a very reduced number of, optimally placed, sampling points, the corresponding weights and placements being evaluated through a greedy algorithm. The resulting low-dimensional and reduced-quadrature variational problem translates into very relevant savings on the computational cost and high computational speed-ups. Particular attention is additionally given to numerical tests and performance evaluations of the new hyper-reduced methodology, by “a-priori” and “a-posteriori” error assessments. Moreover, for the purposes of validation of the present techniques, a real structural problem exhibiting propagating fracture at two-scales is modeled on the basis of the strain injection-based multiscale approach previously developed by the authors. The performance of the proposed strategy, in terms of speed-up vs. error, is deeply analyzed and reported
Abstract
The paper proposes some new computational strategies for affordably solving multiscale fracture problems through a FE2 approach. To take into account the mechanical effects [...]
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On the numerical modeling of granular material flows via the Particle Finite Element Method (PFEM)
C. Dávalos, J. Cante, J. Hernández, J. Oliver

International Journal of Solids and Structures (2015). Vol. 71, pp. 99-125 (Preprint)

Abstract
The aim of this work is to describe a numerical framework for reliably and robustly simulating the different kinematic conditions exhibited by granular materials while spreading ---from a stagnant condition, when the material is at rest, to a transition to granular flow, and back to a deposit profile. The gist of the employed modeling approach was already presented by the authors in a recent work (Cante et al., 2014), but no proper description of the underlying numerical techniques was provided therein. The present paper focuses precisely on the detailed discussion of such numerical techniques, as well as on its rigorous validation with the experimental results obtained by Lajeunesse, et al. in Ref. ( Lajeunesse et al., 2004). The constitutive model is based on the concepts of large strains plasticity. The yield surface is defined in terms of the Drucker Prager yield function, endowed with a deviatoric plastic flow and the elastic part by a hypoelastic model. The plastic flow condition is assumed nearly incompressible, so a u - p mixed formulation, with a stabilization of the pressure term via the Polynomial Pressure Projection (PPP), is employed. The numerical scheme takes as starting point the Particle Finite Element Method (PFEM) in which the spatial domain is continuously redefined by a different nodal reconnection, generated by a Delaunay triangulation. In contrast to classical PFEM approximations ( Idelsohn et al., 2004), in which the free boundary is obtained by a geometrical technique (a-shape method), in this work the boundary is treated as a material surface, and the boundary nodes are removed or inserted by means of an error function. One of the novelties of this work is the use of the so-called Impl-Ex hybrid integration technique to enhance the spectral properties of the algorithmic tangent moduli and thus reduce the number of iterations and robustness of the accompanying Newton-Raphson solution algorithm (compared with fully implicit schemes respectively). The new set of numerical tools implemented in the PFEM algorithm – including new discretization techniques, the use of a projection of the variables between meshes, and the constraint of the free-surface instead using classic a-shape – allows us to eliminate the negative Jacobians present during large deformation problems, which is one of the drawbacks in the simulation of granular flows. Finally, numerical results are compared with the experiments developed in Ref. (Lajeunesse et al., 2004), where a granular mass, initially confined in a cylindrical container, is suddenly allowed to spread by the sudden removal of the container. The study is carried out using different geometries with varying initial aspect ratios. The excellent agreement between computed and experimental results convincingly demonstrates the reliability of the model to reproduce different kinematic conditions in transient and stationary regimes.
Abstract
The aim of this work is to describe a numerical framework for reliably and robustly simulating the different kinematic conditions exhibited by granular materials while spreading [...]
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Retention of Mechanical Properties After Water Immersion for Glass-Fibre Polymer Composite Laminates with Thermoset & Thermoplastic Infusible Resins
N. Nash, C. Sirerol, A. Portela, I. Manolakis, A. Comer

ICCS 21, International Conference on Composite Structures, Bologna, Italy

Abstract
Glass-fibre reinforced polymer (GRP) composite materials are the most widely adopted amongst fibrereinforced polymer composites globally, with approximately 1 million tons produced annually in the EU alone. GRP’s find very wide use and application in a number of industrial sectors (e.g. land & waterborne transport1 , marine, construction) due to their excellent balance between good performance and low cost compared to fibre reinforced polymers utilising other commercially available fibres (e.g. carbon, aramid). Particularly in marine applications, durability of composites and their ability to exhibit unchanged performance and stability in a marine context and environment is a crucial factor in order to select the most appropriate combination of polymer matrix and reinforcement. Ideally, a composite would retain its mechanical and thermo-mechanical profile even when exposed to a marine environment for extended periods. In this work, we conducted an extensive comparative study of the water absorption behavior and retention of mechanical properties of a group of GRP composite laminates manufactured with a range of infusible thermosetting and thermoplastics resins. Sample preparation for water immersion studies was according to ASTM D5229. This study was part of a comprehensive down-selection of commercially available resins in terms of their suitability for shipbuilding applications, as part of the EU H2020 project FIBRESHIP2 . All laminates were manufactured by Vacuum-Assisted Resin Transfer Moulding (VARTM; the most relevant manufacturing technique in shipbuilding) with a range of state-of-the-art thermosetting resins (Urethane acrylate Crestapol 1210, Epoxy SR1125, Bio-epoxy Supersap CLR, Phenolic Cellobond J2027X) and a novel infusible acrylic thermoplastic resin (Acrylic Elium 150). The reinforcement of choice for each laminate was a unidirectional glass fabric of 996 gsm. A selection of relevant properties of the laminates with different resin systems is presented in this paper including fibre volume fraction, apparent interlaminar shear strength (dry and wet condition), flexural strength (dry and wet condition) and flexural modulus (dry and wet condition). For the wet condition, samples were immersed in distilled water for 28 days at 35 oC (wet state) in accordance with classification society guidelines. The quality of the laminates (void content, fibre-matrix adhesion) was examined by scanning electron microscopy on fracture surfaces. The effects of water absorption on the microstructure, mechanical, thermal & thermomechanical properties of the laminates were studied. The average water absorption percentage varied across all resins systems from 0.19 to 1.37% in the interlaminar-shear specimens, and from 0.25 to 1.59% in the flexure specimens. The phenolic laminate was the one absorbing most water in both cases but the mechanical properties were relatively unaffected. Fibre volume fraction was in the range 0.56 to 0.6 for all of the laminates. The majority of the tested GRP laminates showed good retention of their flexural properties and interlaminar shear strength under the testing conditions. The laminate that appeared to be most adversely affected was the infusible thermoplastic, showing a reduction in flexural strength and interlaminar shear strength of 17.3% and 37.5%, respectively (in comparison to the dry state values). However, the water absorption for the Elium 150 was not excessive, ranging from 0.40 to 0.42% for the ILSS and flexure samples, respectively. References: 1 Summerscales J, Marine applications of advanced fibre reinforced composites, Woodhead Publishing, Cambridge, 2016 2 H2020 project FIBRESHIP, funded by the European Commission under GA 723360 (www.fibreship.eu)
Abstract
Glass-fibre reinforced polymer (GRP) composite materials are the most widely adopted amongst fibrereinforced polymer composites globally, with approximately 1 million tons [...]
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Experimental Investigation on the effect of water ingress on the flexural and interlaminar properties of glass/vinylester composite for marine applications
A. Portela, N. Nash, C. Sirerol, I. Manolakis, A. Comer

Conference on Marine Aging of Polymers and mechanical performance, Brest, France

Abstract
Fibre-reinforced polymer (FRP) composite materials find increasing acceptance and application in a number of transport sectors due to their lightweight nature, which provides a significant advantage in terms of lower fuel consumption and greenhouse gas emissions, in line with relevant EU directives. Particularly in the marine industry, FRPs are currently dominating the manufacture of vessels up to 50 m in length, with liquid resin infusion (LRI) being the most frequently used manufacturing technique and vacuum-assisted resin transfer moulding (VARTM) in particular the most widely adopted LRI variant. The wide-scale adoption of FRPs into large marine structures is often hindered by the lack of guidelines available for qualification of these materials by classification societies, particularly in relation to fire safety. FIBRESHIP is a Horizon 2020 funded EU project that aims to further the use of FRPs in long-length ship construction by addressing this issue in addition to tackling numerous other challenges associated with manufacturing FRP composite ships. It is important to characterise fully the performance of new commercially available marine resin systems as a potential candidates for selection in composite ship construction. This needs to be done under a wide range of environmental conditions, as durability of composites and their ability to exhibit unchanged performance and stability in a marine context and environment is a crucial factor in their selection. Ideally, a composite would retain its mechanical and thermo-mechanical profile even when exposed to a marine environment for extended periods. During the service life of marine composites (typically 20-25 years), water uptake is inevitable. This may cause plasticization, swelling, matrix hydrolysis or debonding of fibres from the matrix. As a result, the mechanical and thermal properties degrade accordingly, and the service life is shortened. This work represents part of a selection process for materials for the construction of long-length ships from FRPs and focuses on a commercially available fireretardant composite system (SAERTEX LEO®). The aim of the study is, therefore, to compare the flexural (ISO 14125) and interlaminar shear (ISO 14130) properties of the SAERTEX LEO® composite system under dry conditions and under “wet” conditions where the specimens have been immersed in deionised water at 35°C for varying durations (28 days, two months, three months). The flexural and interlaminar properties will also be assessed after soaking for 28 days, two months and three months followed by a drying process to remove all ingressed water. This will give an indication of the reversibility of the effects of water ingress and highlight the point at which permanent alteration of the properties begins to occur. Unidirectional laminates are manufactured by VARTM using the Saertex LEO Glass/Vinyl ester system (the system includes a fire-retardant gel coat, however the gel coat was not applied for the purpose of obtaining the mechanical properties of the FRP component of the system only). Dynamic Mechanical Analysis (DMA) is performed to establish that the laminates have been fully cured and fracture mechanisms are examined using scanning electron microscopy.
Abstract
Fibre-reinforced polymer (FRP) composite materials find increasing acceptance and application in a number of transport sectors due to their lightweight nature, which provides [...]
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Experimental Investigation on the effect of thickness on the flexural properties of glass/vinyl-ester composite laminates for marine applications
N. Nash, A. Portela, C. Sirerol, I. Manolakis, A. Comer

MECHCOMP, 5th international Conference on Mechanics of Composites, Lisbon, Portugal

Abstract
Fibre-reinforced polymer (FRP) composite materials find increasing acceptance and application in a number of transport sectors (aviation, land & waterborne transport) due to their lightweight nature, which provides a significant advantage in terms of lower fuel consumption and greenhouse gas emissions, in line with relevant EU directives. Particularly in waterborne transport and shipbuilding, FRP composites are currently dominating the manufacture of vessels up to 50 m in length, with liquid resin infusion (LRI) being the most frequently used manufacturing technique and vacuum-assisted resin transfer moulding (VARTM) in particular the most widely adopted LRI variant. The wide-scale adoption of FRP composites into large marine structures is often hindered by the lack of guidelines available for qualification of these materials by classification societies. FIBRESHIP is a Horizon 2020 funded EU project that aims to further the use of FRP composites in long-length ship construction by addressing this issue in addition to tackling numerous other challenges associated with manufacturing FRP composite ships. This work represents part of a selection process for materials for the construction of long-length ships from FRP composites and focuses on a commercially available fire-retardant composite system (SAERTEX LEO®). As part of the selection procedure for these materials, material properties, such as the flexural strength and modulus, are obtained using coupon-sized test-pieces and are subsequently used as the basis for numerical models for ship design. However, the actual material that is used in the final ship structure is significantly thicker than the coupons from which the original material properties were derived. Additionally, the scale of the manufacturing process of laminates for the extraction of coupons is drastically different to that of the manufacturing process of a ship’s hull. The aim of the study is, therefore, to compare the flexural properties obtained from a thin monolithic laminate manufactured in a research laboratory (University of Limerick, Ireland) to the flexural properties obtained from a thick monolithic laminate representative of the thickness of a ship hull manufactured in a shipyard (iXBlue Division H2x, Marseille, France) using the same material under investigation. This will give an indication of how representative the thin test coupons are of the material manufactured by the shipyards at the thickness used in the final structure. Unidirectional laminates are manufactured in both the research and shipyard facilities by VARTM using the Saertex LEO Glass/Vinyl ester system (the system includes a fire-retardant gel coat, however the gel coat was not applied for the purpose of obtaining the mechanical properties of the FRP component of the system only). Dynamic Mechanical Analysis (DMA) is performed on specimens from the thin and thick laminates to establish that the laminates have been fully cured. Three-point-bend tests in accordance with ISO 14125 are performed on 0° and 90° specimens extracted from thin and thick laminates. Another set of 0° and 90° specimens extracted from thin and thick laminates are tested according to Bureau Veritas guidelines (NR456) in order to investigate the comparison between the properties obtained using both methods. Fracture mechanisms in thick and thin specimens are examined using scanning electron microscopy.
Abstract
Fibre-reinforced polymer (FRP) composite materials find increasing acceptance and application in a number of transport sectors (aviation, land & waterborne transport) [...]
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Mechanical characterization of polymer composite materials for long length ships
T. Gobikannan, A. Portela, C. Athavale, A. Comer, A. Haldar

Open Access Repository of the FIBRESHIP project (2020). 10

Abstract
In the marine industry, Fibre-reinforced polymers (FRP) are currently dominating the manufacture of vessels up to 50m in length, with liquid resin infusion (LRI) being the most frequently used manufacturing technique, of which vacuum-assisted liquid resin infusion is the most widely adopted LRI variant. However, current regulations restrict the use of composite materials in vessels over 50m in length. FIBRESHIP is a Horizon 2020 funded EU project that aims to further the use of FRPs in vessels over 50m in length by addressing the regulatory restrictions and the numerous other challenges associated with manufacturing long-length FRP composite ships. The mechanical performance of new commercially available composite material constituents as potential candidates for selection in composite ship construction is central to this work. This paper provides an overview of selected work performed as part of the FIBRESHIP project in terms of evaluating various mechanical properties of selected laminates under dry and wet conditions. The laminates were immersed in seawater at 35°C for durations of one to three months. Three-point bend and interlaminar shear strength tests were undertaken in order to investigate the change in the mechanical properties of composite laminates subject to immersion. Finally, tested specimens were observed using micro-computed tomography (μCT) to evaluate the failure morphology.
Abstract
In the marine industry, Fibre-reinforced polymers (FRP) are currently dominating the manufacture of vessels up to 50m in length, with liquid resin infusion (LRI) being the [...]
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Continuum approach to computational multiscale modeling of propagating fracture
J. Oliver, M. Caicedo, M. Roubin, A. Huespe, J. Hernández

Computer Methods in Applied Mechanics and Engineering (2015). Vol. 294, pp. 384-427

Abstract
A new approach to two-scale modeling of propagating fracture, based on computational homogenization (FE2), is presented. The specific features of the approach are: a) a continuum setting for representation of the fracture at both scales based on the Continuum Strong Discontinuity Approach (CSDA), and b) the use, for the considered non-smooth (discontinuous) problem, of the same computational homogenization framework than for classical smooth cases. As a key issue, the approach retrieves a characteristic length computed at the lower scale, which is exported to the upper one and used therein as a regularization parameter for a propagating strong discontinuity kinematics. This guarantees the correct transfer of fracture energy between scales and the proper dissipation at the upper scale. Representative simulations show that the resulting formulation provides consistent results, which are objective with respect to, both, size and bias of the upper-scale mesh, and with respect to the size of the lower-scale RVE/failure cell, as well as the capability to model propagating cracks at the upper scale, in combination with crack-path-field and strain injection techniques. The continuum character of the approach confers to the formulation a minimal invasive character, with respect to standard procedures for multi-scale computational homogenization
Abstract
A new approach to two-scale modeling of propagating fracture, based on computational homogenization (FE2), is presented. The specific features of the approach are: a) a continuum [...]
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Continuum approach to computational multi-scale modeling of fracture
J. Oliver, M. Caicedo, E. Roubin, A. Huespe

Key engineering materials (2014). Vol. 627, pp. 349-352 (Preprint)

Abstract
This paper presents a FE2 multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials. The model is assessed by application to cementitious materials. Using the Continuum Strong Discontinuity Approach (CSD), innovative numerical tools, such as strain injection and crack path field techniques, provide a robust, and mesh-size, mesh-bias and RVE-size objective, procedure to model crack onset and propagation at the macro-scale
Abstract
This paper presents a FE2 multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials. The model is assessed by application [...]
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High-performance model reduction techniques in computational multiscale homogenization
J. Hernández, J. Oliver, A. Huespe, M. Caicedo, J. Cante

Computer Methods in Applied Mechanics and Engineering (2014). Vol. 276, pp. 149-189 (Preprint)

Abstract
A novel model-order reduction technique for the solution of the fine-scale equilibrium problem appearing in computational homogenization is presented. The reduced set of empirical shape functions is obtained using a partitioned version that accounts for the elastic/inelastic character of the solution - of the Proper Orthogonal Decomposition (POD). On the other hand, it is shown that the standard approach of replacing the nonaffine term by an interpolant constructed using only POD modes leads to ill-posed formulations. We demonstrate that this ill-posedness can be avoided by enriching the approximation space with the span of the gradient of the empirical shape functions. Furthermore, interpolation points are chosen guided, not only by accuracy requirements, but also by stability considerations. The approach is assessed in the homogenization of a highly complex porous metal material. Computed results show that computational complexity is independent of the size and geometrical complexity of the Representative Volume Element. The speedup factor is over three orders of magnitude - as compared with finite element analysis - whereas the maximum error in stresses is less than 10%. A novel model-order reduction technique for the solution of the fine-scale equilibrium problem appearing in computational homogenization is presented. The reduced set of empirical shape functions is obtained using a partitioned version that accounts for the elastic/inelastic character of the solution - of the Proper Orthogonal Decomposition (POD). On the other hand, it is shown that the standard approach of replacing the nonaffine term by an interpolant constructed using only POD modes leads to ill-posed formulations. We demonstrate that this ill-posedness can be avoided by enriching the approximation space with the span of the gradient of the empirical shape functions. Furthermore, interpolation points are chosen guided, not only by accuracy requirements, but also by stability considerations. The approach is assessed in the homogenization of a highly complex porous metal material. Computed results show that computational complexity is independent of the size and geometrical complexity of the Representative Volume Element. The speedup factor is over three orders of magnitude - as compared with finite element analysis - whereas the maximum error in stresses is less than 10%.
Abstract
A novel model-order reduction technique for the solution of the fine-scale equilibrium problem appearing in computational homogenization is presented. The reduced set of empirical [...]
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